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Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and
determinants In mathematics, the determinant is a scalar value that is a function of the entries of a square matrix. It characterizes some properties of the matrix and the linear map represented by the matrix. In particular, the determinant is nonzero if and ...
of health and disease conditions in a defined
population Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction using a ...
. It is a cornerstone of
public health Public health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals". Analyzing the det ...
, and shapes policy decisions and
evidence-based practice Evidence-based practice (EBP) is the idea that occupational practices ought to be based on scientific evidence. While seemingly obviously desirable, the proposal has been controversial, with some arguing that results may not specialize to indiv ...
by identifying
risk factor In epidemiology, a risk factor or determinant is a variable associated with an increased risk of disease or infection. Due to a lack of harmonization across disciplines, determinant, in its more widely accepted scientific meaning, is often use ...
s for disease and targets for
preventive healthcare Preventive healthcare, or prophylaxis, consists of measures taken for the purposes of disease prevention.Hugh R. Leavell and E. Gurney Clark as "the science and art of preventing disease, prolonging life, and promoting physical and mental hea ...
. Epidemiologists help with study design, collection, and
statistical analysis Statistical inference is the process of using data analysis to infer properties of an underlying distribution of probability.Upton, G., Cook, I. (2008) ''Oxford Dictionary of Statistics'', OUP. . Inferential statistical analysis infers propertie ...
of data, amend interpretation and dissemination of results (including
peer review Peer review is the evaluation of work by one or more people with similar competencies as the producers of the work (peers). It functions as a form of self-regulation by qualified members of a profession within the relevant field. Peer review ...
and occasional
systematic review A systematic review is a Literature review, scholarly synthesis of the evidence on a clearly presented topic using critical methods to identify, define and assess research on the topic. A systematic review extracts and interprets data from publ ...
). Epidemiology has helped develop
methodology In its most common sense, methodology is the study of research methods. However, the term can also refer to the methods themselves or to the philosophical discussion of associated background assumptions. A method is a structured procedure for bri ...
used in
clinical research Clinical research is a branch of healthcare science that determines the safety and effectiveness ( efficacy) of medications, devices, diagnostic products and treatment regimens intended for human use. These may be used for prevention, treatm ...
,
public health Public health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals". Analyzing the det ...
studies, and, to a lesser extent,
basic research Basic research, also called pure research or fundamental research, is a type of scientific research with the aim of improving scientific theories for better understanding and prediction of natural or other phenomena. In contrast, applied resear ...
in the biological sciences. Major areas of epidemiological study include disease causation,
transmission Transmission may refer to: Medicine, science and technology * Power transmission ** Electric power transmission ** Propulsion transmission, technology allowing controlled application of power *** Automatic transmission *** Manual transmission *** ...
,
outbreak In epidemiology, an outbreak is a sudden increase in occurrences of a disease when cases are in excess of normal expectancy for the location or season. It may affect a small and localized group or impact upon thousands of people across an entire ...
investigation,
disease surveillance Disease surveillance is an epidemiological practice by which the spread of disease is monitored in order to establish patterns of progression. The main role of disease surveillance is to predict, observe, and minimize the harm caused by outbreak, ...
,
environmental epidemiology Environmental epidemiology is a branch of epidemiology concerned with determining how environmental exposures impact human health. This field seeks to understand how various external risk factors may predispose to or protect against disease, illnes ...
,
forensic epidemiology The discipline of forensic epidemiology (FE) is a hybrid of principles and practices common to both forensic medicine and epidemiology. FE is directed at filling the gap between clinical judgment and epidemiologic data for determinations of causal ...
,
occupational epidemiology Occupational epidemiology is a subdiscipline of epidemiology that focuses on investigations of workers and the workplace. Occupational epidemiologic studies examine health outcomes among workers, and their potential association with conditions in ...
,
screening Screening may refer to: * Screening cultures, a type a medical test that is done to find an infection * Screening (economics), a strategy of combating adverse selection (includes sorting resumes to select employees) * Screening (environmental), a ...
,
biomonitoring In analytical chemistry, biomonitoring is the measurement of the body burden of toxic chemical compounds, elements, or their metabolites, in biological substances. Often, these measurements are done in blood and urine. Biomonitoring is performed ...
, and comparisons of treatment effects such as in
clinical trials Clinical trials are prospective biomedical or behavioral research studies on human participants designed to answer specific questions about biomedical or behavioral interventions, including new treatments (such as novel vaccines, drugs, dietar ...
. Epidemiologists rely on other scientific disciplines like
biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary i ...
to better understand disease processes,
statistics Statistics (from German language, German: ''wikt:Statistik#German, Statistik'', "description of a State (polity), state, a country") is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of ...
to make efficient use of the data and draw appropriate conclusions,
social science Social science is one of the branches of science, devoted to the study of societies and the relationships among individuals within those societies. The term was formerly used to refer to the field of sociology, the original "science of soc ...
s to better understand proximate and distal causes, and
engineering Engineering is the use of scientific method, scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of engineering encompasses a broad rang ...
for
exposure assessment Exposure assessment is a branch of environmental science and occupational hygiene that focuses on the processes that take place at the interface between the environment containing the contaminant of interest and the organism being considered. ...
. ''Epidemiology'', literally meaning "the study of what is upon the people", is derived , suggesting that it applies only to human populations. However, the term is widely used in studies of zoological populations (veterinary epidemiology), although the term "
epizoology Epizootiology, epizoology, or veterinary epidemiology is the study of disease patterns within animal populations. See also * Epizootic In epizoology, an epizootic (from Greek: ''epi-'' upon + ''zoon'' animal) is a disease event in a nonhuman anim ...
" is available, and it has also been applied to studies of plant populations (botanical or
plant disease epidemiology Plant disease epidemiology is the study of disease in plant populations. Much like diseases of humans and other animals, plant diseases occur due to pathogens such as bacteria, viruses, fungi, oomycetes, nematodes, phytoplasmas, protozoa, and paras ...
). The distinction between "epidemic" and "endemic" was first drawn by
Hippocrates Hippocrates of Kos (; grc-gre, Ἱπποκράτης ὁ Κῷος, Hippokrátēs ho Kôios; ), also known as Hippocrates II, was a Greek physician of the classical period who is considered one of the most outstanding figures in the history of ...
, to distinguish between diseases that are "visited upon" a population (epidemic) from those that "reside within" a population (endemic).Carol Buck, Alvaro Llopis; Enrique Nájera; Milton Terris (1998) ''The Challenge of Epidemiology: Issues and Selected Readings''. Scientific Publication No. 505. Pan American Health Organization. Washington, DC. p. 3. The term "epidemiology" appears to have first been used to describe the study of epidemics in 1802 by the Spanish physician Villalba in ''Epidemiología Española''. Epidemiologists also study the interaction of diseases in a population, a condition known as a
syndemic A syndemic or synergistic epidemic is the aggregation of two or more concurrent or sequential epidemics or disease clusters in a population with biological interactions, which exacerbate the prognosis and burden of disease. The term was develo ...
. The term epidemiology is now widely applied to cover the description and causation of not only epidemic, infectious disease, but of disease in general, including related conditions. Some examples of topics examined through epidemiology include as high blood pressure, mental illness and
obesity Obesity is a medical condition, sometimes considered a disease, in which excess body fat has accumulated to such an extent that it may negatively affect health. People are classified as obese when their body mass index (BMI)—a person's we ...
. Therefore, this epidemiology is based upon how the pattern of the disease causes change in the function of human beings.


History

The Greek physician
Hippocrates Hippocrates of Kos (; grc-gre, Ἱπποκράτης ὁ Κῷος, Hippokrátēs ho Kôios; ), also known as Hippocrates II, was a Greek physician of the classical period who is considered one of the most outstanding figures in the history of ...
, known as the father of
medicine Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care pract ...
, sought a logic to sickness; he is the first person known to have examined the relationships between the occurrence of disease and environmental influences. Hippocrates believed sickness of the human body to be caused by an imbalance of the four
humors Humorism, the humoral theory, or humoralism, was a system of medicine detailing a supposed makeup and workings of the human body, adopted by Ancient Greek and Roman physicians and philosophers. Humorism began to fall out of favor in the 1850s ...
(black bile, yellow bile, blood, and phlegm). The cure to the sickness was to remove or add the humor in question to balance the body. This belief led to the application of bloodletting and dieting in medicine.Merril, Ray M., PhD, MPH. (2010): ''An Introduction to Epidemiology'', Fifth Edition. Chapter 2: "Historic Developments in Epidemiology". Jones and Bartlett Publishing He coined the terms ''endemic'' (for diseases usually found in some places but not in others) and ''
epidemic An epidemic (from Ancient Greek, Greek ἐπί ''epi'' "upon or above" and δῆμος ''demos'' "people") is the rapid spread of disease to a large number of patients among a given population within an area in a short period of time. Epidemics ...
'' (for diseases that are seen at some times but not others).


Modern era

In the middle of the 16th century, a doctor from
Verona Verona ( , ; vec, Verona or ) is a city on the Adige River in Veneto, Northern Italy, Italy, with 258,031 inhabitants. It is one of the seven provincial capitals of the region. It is the largest city Comune, municipality in the region and the ...
named
Girolamo Fracastoro Girolamo Fracastoro ( la, Hieronymus Fracastorius; c. 1476/86 August 1553) was an Italian physician, poet, and scholar in mathematics, geography and astronomy. Fracastoro subscribed to the philosophy of atomism, and rejected appeals to hidden c ...
was the first to propose a theory that these very small, unseeable, particles that cause disease were alive. They were considered to be able to spread by air, multiply by themselves and to be destroyable by fire. In this way he refuted
Galen Aelius Galenus or Claudius Galenus ( el, Κλαύδιος Γαληνός; September 129 – c. AD 216), often Anglicized as Galen () or Galen of Pergamon, was a Greek physician, surgeon and philosopher in the Roman Empire. Considered to be one of ...
's
miasma theory The miasma theory (also called the miasmatic theory) is an obsolete medical theory that held that diseases—such as cholera, chlamydia, or the Black Death—were caused by a ''miasma'' (, Ancient Greek for 'pollution'), a noxious form of "bad ...
(poison gas in sick people). In 1543 he wrote a book '' De contagione et contagiosis morbis'', in which he was the first to promote personal and environmental
hygiene Hygiene is a series of practices performed to preserve health. According to the World Health Organization (WHO), "Hygiene refers to conditions and practices that help to maintain health and prevent the spread of diseases." Personal hygiene refer ...
to prevent disease. The development of a sufficiently powerful microscope by
Antonie van Leeuwenhoek Antonie Philips van Leeuwenhoek ( ; ; 24 October 1632 – 26 August 1723) was a Dutch microbiologist and microscopist in the Golden Age of Dutch science and technology. A largely self-taught man in science, he is commonly known as " the ...
in 1675 provided visual evidence of living particles consistent with a
germ theory of disease The germ theory of disease is the currently accepted scientific theory for many diseases. It states that microorganisms known as pathogens or "germs" can lead to disease. These small organisms, too small to be seen without magnification, invade h ...
. During the
Ming Dynasty The Ming dynasty (), officially the Great Ming, was an Dynasties in Chinese history, imperial dynasty of China, ruling from 1368 to 1644 following the collapse of the Mongol Empire, Mongol-led Yuan dynasty. The Ming dynasty was the last ort ...
, Wu Youke (1582–1652) developed the idea that some diseases were caused by transmissible agents, which he called ''Li Qi'' (戾气 or pestilential factors) when he observed various epidemics rage around him between 1641 and 1644. His book ''Wen Yi Lun'' (瘟疫论,Treatise on Pestilence/Treatise of Epidemic Diseases) can be regarded as the main etiological work that brought forward the concept. His concepts were still being considered in analysing SARS outbreak by WHO in 2004 in the context of traditional Chinese medicine. Another pioneer,
Thomas Sydenham Thomas Sydenham (10 September 1624 – 29 December 1689) was an English physician. He was the author of ''Observationes Medicae'' which became a standard textbook of medicine for two centuries so that he became known as 'The English Hippocrate ...
(1624–1689), was the first to distinguish the fevers of Londoners in the later 1600s. His theories on cures of fevers met with much resistance from traditional physicians at the time. He was not able to find the initial cause of the
smallpox Smallpox was an infectious disease caused by variola virus (often called smallpox virus) which belongs to the genus Orthopoxvirus. The last naturally occurring case was diagnosed in October 1977, and the World Health Organization (WHO) c ...
fever he researched and treated.
John Graunt John Graunt (24 April 1620 – 18 April 1674) has been regarded as the founder of demography. Graunt was one of the first demographers, and perhaps the first epidemiologist, though by profession he was a haberdasher. He was bankrupted later in li ...
, a
haberdasher In British English, a haberdasher is a business or person who sells small articles for sewing, dressmaking and knitting, such as buttons, ribbons, and zippers; in the United States, the term refers instead to a retailer who sells men's clothing, ...
and amateur statistician, published ''Natural and Political Observations ... upon the Bills of Mortality'' in 1662. In it, he analysed the mortality rolls in
London London is the capital and largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary down to the North Sea, and has been a majo ...
before the
Great Plague The Black Death (also known as the Pestilence, the Great Mortality or the Plague) was a bubonic plague pandemic occurring in Western Eurasia and North Africa from 1346 to 1353. It is the most fatal pandemic recorded in human history, causi ...
, presented one of the first
life tables In actuarial science and demography, a life table (also called a mortality table or actuarial table) is a table which shows, for each age, what the probability is that a person of that age will die before their next birthday ("probability of deat ...
, and reported time trends for many diseases, new and old. He provided statistical evidence for many theories on disease, and also refuted some widespread ideas on them.
John Snow John Snow (15 March 1813 – 16 June 1858) was an English physician and a leader in the development of anaesthesia and medical hygiene. He is considered one of the founders of modern epidemiology, in part because of his work in tracing the so ...
is famous for his investigations into the causes of the 19th-century
cholera Cholera is an infection of the small intestine by some strains of the bacterium ''Vibrio cholerae''. Symptoms may range from none, to mild, to severe. The classic symptom is large amounts of watery diarrhea that lasts a few days. Vomiting and ...
epidemics, and is also known as the father of (modern) epidemiology. He began with noticing the significantly higher death rates in two areas supplied by Southwark Company. His identification of the Broad Street pump as the cause of the Soho epidemic is considered the classic example of epidemiology. Snow used chlorine in an attempt to clean the water and removed the handle; this ended the outbreak. This has been perceived as a major event in the history of
public health Public health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals". Analyzing the det ...
and regarded as the founding event of the science of epidemiology, having helped shape public health policies around the world. However, Snow's research and preventive measures to avoid further outbreaks were not fully accepted or put into practice until after his death due to the prevailing
Miasma Theory The miasma theory (also called the miasmatic theory) is an obsolete medical theory that held that diseases—such as cholera, chlamydia, or the Black Death—were caused by a ''miasma'' (, Ancient Greek for 'pollution'), a noxious form of "bad ...
of the time, a model of disease in which poor air quality was blamed for illness. This was used to rationalize high rates of infection in impoverished areas instead of addressing the underlying issues of poor nutrition and sanitation, and was proven false by his work. Other pioneers include Danish physician
Peter Anton Schleisner Peter may refer to: People * List of people named Peter, a list of people and fictional characters with the given name * Peter (given name) ** Saint Peter (died 60s), apostle of Jesus, leader of the early Christian Church * Peter (surname), a sur ...
, who in 1849 related his work on the prevention of the epidemic of
neonatal tetanus Neonatal tetanus (''trismus nascentium'') is a form of generalised tetanus that occurs in newborns. Infants who have not acquired passive immunity from an immunized mother are at risk. It usually occurs through infection of the unhealed umbilical ...
on the
Vestmanna Islands Vestmannaeyjar (, sometimes anglicized as Westman Islands) is a municipality and archipelago off the south coast of Iceland. The largest island, Heimaey, has a population of 4,414, most of whom live in the archipelago's main town, Vestmannaeyj ...
in
Iceland Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its s ...
. Another important pioneer was Hungarian physician
Ignaz Semmelweis Ignaz Philipp Semmelweis (; hu, Semmelweis Ignác Fülöp ; 1 July 1818 – 13 August 1865) was a Hungarian physician and scientist, who was an early pioneer of antiseptic procedures. Described as the "saviour of mothers", he discovered that t ...
, who in 1847 brought down infant mortality at a Vienna hospital by instituting a disinfection procedure. His findings were published in 1850, but his work was ill-received by his colleagues, who discontinued the procedure. Disinfection did not become widely practiced until British surgeon
Joseph Lister Joseph Lister, 1st Baron Lister, (5 April 182710 February 1912) was a British surgeon, medical scientist, experimental pathologist and a pioneer of antiseptic surgery and preventative medicine. Joseph Lister revolutionised the craft of s ...
'discovered'
antiseptics An antiseptic (from Greek ἀντί ''anti'', "against" and σηπτικός ''sēptikos'', "putrefactive") is an antimicrobial substance or compound that is applied to living tissue/skin to reduce the possibility of infection, sepsis, or putre ...
in 1865 in light of the work of
Louis Pasteur Louis Pasteur (, ; 27 December 1822 – 28 September 1895) was a French chemist and microbiologist renowned for his discoveries of the principles of vaccination, microbial fermentation and pasteurization, the latter of which was named afte ...
. In the early 20th century, mathematical methods were introduced into epidemiology by
Ronald Ross Sir Ronald Ross (13 May 1857 – 16 September 1932) was a British medical doctor who received the Nobel Prize for Physiology or Medicine in 1902 for his work on the transmission of malaria, becoming the first British Nobel laureate, and the f ...
,
Janet Lane-Claypon Janet Elizabeth Lane-Claypon, Lady Forber (3 February 1877 – 17 July 1967) was an English physician. She was one of the founders of the science of epidemiology, pioneering the use of cohort studies and case-control studies. Early life and ...
,
Anderson Gray McKendrick Lt Col Anderson Gray McKendrick DSc FRSE (8 September 1876 – 30 May 1943) was a Scottish military physician and epidemiologist who pioneered the use of mathematical methods in epidemiology. Irwin (see below) commented on the quality of his wor ...
, and others. In a parallel development during the 1920s, German-Swiss pathologist
Max Askanazy Max Askanazy (24 February 1865, Stallupönen, East Prussia – 23 October 1940, Geneva, Switzerland) was a German-Swiss pathologist. In 1890 he received his medical doctorate from the University of Königsberg, where he worked for several years ...
and others founded the International Society for Geographical Pathology to systematically investigate the geographical pathology of cancer and other non-infectious diseases across populations in different regions. After World War II,
Richard Doll Sir William Richard Shaboe Doll (28 October 1912 – 24 July 2005) was a British physician who became an epidemiologist in the mid-20th century and made important contributions to that discipline. He was a pioneer in research linking smoking ...
and other non-pathologists joined the field and advanced methods to study cancer, a disease with patterns and mode of occurrences that could not be suitably studied with the methods developed for epidemics of infectious diseases. Geography pathology eventually combined with infectious disease epidemiology to make the field that is epidemiology today. Another breakthrough was the 1954 publication of the results of a British Doctors Study, led by
Richard Doll Sir William Richard Shaboe Doll (28 October 1912 – 24 July 2005) was a British physician who became an epidemiologist in the mid-20th century and made important contributions to that discipline. He was a pioneer in research linking smoking ...
and
Austin Bradford Hill Sir Austin Bradford Hill (8 July 1897 – 18 April 1991) was an English epidemiologist and statistician, pioneered the randomised clinical trial and, together with Richard Doll, demonstrated the connection between cigarette smoking and lung c ...
, which lent very strong statistical support to the link between
tobacco smoking Tobacco smoking is the practice of burning tobacco and ingesting the resulting smoke. The smoke may be inhaled, as is done with cigarettes, or simply released from the mouth, as is generally done with pipes and cigars. The practice is believed ...
and
lung cancer Lung cancer, also known as lung carcinoma (since about 98–99% of all lung cancers are carcinomas), is a malignant lung tumor characterized by uncontrolled cell growth in tissue (biology), tissues of the lung. Lung carcinomas derive from tran ...
. In the late 20th century, with the advancement of biomedical sciences, a number of molecular markers in blood, other biospecimens and environment were identified as predictors of development or risk of a certain disease. Epidemiology research to examine the relationship between these
biomarker In biomedical contexts, a biomarker, or biological marker, is a measurable indicator of some biological state or condition. Biomarkers are often measured and evaluated using blood, urine, or soft tissues to examine normal biological processes, ...
s analyzed at the molecular level and disease was broadly named "
molecular epidemiology Molecular epidemiology is a branch of epidemiology and medical science that focuses on the contribution of potential genetic and environmental risk factors, identified at the molecular level, to the etiology, distribution and prevention of disease ...
". Specifically, "
genetic epidemiology Genetic epidemiology is the study of the role of genetic factors in determining health and disease in families and in populations, and the interplay of such genetic factors with environmental factors. Genetic epidemiology seeks to derive a statist ...
" has been used for epidemiology of germline genetic variation and disease. Genetic variation is typically determined using DNA from peripheral blood leukocytes.


21st century

Since the 2000s,
genome-wide association studies In genomics, a genome-wide association study (GWA study, or GWAS), also known as whole genome association study (WGA study, or WGAS), is an observational study of a genome-wide set of genetic variants in different individuals to see if any varian ...
(GWAS) have been commonly performed to identify genetic risk factors for many diseases and health conditions. While most molecular epidemiology studies are still using conventional disease
diagnosis Diagnosis is the identification of the nature and cause of a certain phenomenon. Diagnosis is used in many different disciplines, with variations in the use of logic, analytics, and experience, to determine " cause and effect". In systems engin ...
and classification systems, it is increasingly recognized that disease progression represents inherently heterogeneous processes differing from person to person. Conceptually, each individual has a unique disease process different from any other individual ("the unique disease principle"), considering uniqueness of the
exposome An environmental factor, ecological factor or eco factor is any factor, abiotic or biotic, that influences living organisms. Abiotic factors include ambient temperature, amount of sunlight, and pH of the water soil in which an organism lives. Bi ...
(a totality of endogenous and exogenous / environmental exposures) and its unique influence on molecular pathologic process in each individual. Studies to examine the relationship between an exposure and molecular pathologic signature of disease (particularly
cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
) became increasingly common throughout the 2000s. However, the use of
molecular pathology Molecular pathology is an emerging discipline within pathology which is focused in the study and diagnosis of disease through the examination of molecules within organs, tissues or bodily fluids. Molecular pathology shares some aspects of practice ...
in epidemiology posed unique challenges, including lack of research guidelines and standardized
statistical Statistics (from German: ''Statistik'', "description of a state, a country") is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data. In applying statistics to a scientific, industria ...
methodologies, and paucity of interdisciplinary experts and training programs. Furthermore, the concept of disease heterogeneity appears to conflict with the long-standing premise in epidemiology that individuals with the same disease name have similar etiologies and disease processes. To resolve these issues and advance population health science in the era of molecular
precision medicine Precision, precise or precisely may refer to: Science, and technology, and mathematics Mathematics and computing (general) * Accuracy and precision, measurement deviation from true value and its scatter * Significant figures, the number of digit ...
, "molecular pathology" and "epidemiology" was integrated to create a new interdisciplinary field of "
molecular pathological epidemiology Molecular pathological epidemiology (MPE, also molecular pathologic epidemiology) is a discipline combining epidemiology and pathology. It is defined as "epidemiology of molecular pathology and heterogeneity of disease". Pathology and epidemiology s ...
" (MPE), defined as "epidemiology of molecular pathology and heterogeneity of disease". In MPE, investigators analyze the relationships between (A) environmental, dietary, lifestyle and genetic factors; (B) alterations in cellular or extracellular molecules; and (C) evolution and progression of disease. A better understanding of heterogeneity of disease
pathogenesis Pathogenesis is the process by which a disease or disorder develops. It can include factors which contribute not only to the onset of the disease or disorder, but also to its progression and maintenance. The word comes from Greek πάθος ''pat ...
will further contribute to elucidate
etiologies Cause, also known as etiology () and aetiology, is the reason or origination of something. The word ''etiology'' is derived from the Greek , ''aitiologia'', "giving a reason for" (, ''aitia'', "cause"; and , ''-logia''). Description In medicine, ...
of disease. The MPE approach can be applied to not only neoplastic diseases but also non-neoplastic diseases. The concept and paradigm of MPE have become widespread in the 2010s. By 2012, it was recognized that many pathogens'
evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
is rapid enough to be highly relevant to epidemiology, and that therefore much could be gained from an interdisciplinary approach to infectious disease integrating epidemiology and
molecular evolution Molecular evolution is the process of change in the sequence composition of cellular molecules such as DNA, RNA, and proteins across generations. The field of molecular evolution uses principles of evolutionary biology and population genetics ...
to "inform control strategies, or even patient treatment." Modern epidemiological studies can use advanced statistics and
machine learning Machine learning (ML) is a field of inquiry devoted to understanding and building methods that 'learn', that is, methods that leverage data to improve performance on some set of tasks. It is seen as a part of artificial intelligence. Machine ...
to create predictive models as well as to define treatment effects.


Types of studies

Epidemiologists employ a range of study designs from the observational to experimental and generally categorized as descriptive (involving the assessment of data covering time, place, and person), analytic (aiming to further examine known associations or hypothesized relationships), and experimental (a term often equated with clinical or community trials of treatments and other interventions). In observational studies, nature is allowed to "take its course", as epidemiologists observe from the sidelines. Conversely, in experimental studies, the epidemiologist is the one in control of all of the factors entering a certain case study."Principles of Epidemiology." Key Concepts in Public Health. London: Sage UK, 2009. Credo Reference. 1 August 2011. Web. 30 September 2012. Epidemiological studies are aimed, where possible, at revealing unbiased relationships between exposures such as alcohol or smoking,
biological agents A biological agent (also called bio-agent, biological threat agent, biological warfare agent, biological weapon, or bioweapon) is a bacterium, virus, protozoan, parasite, fungus, or toxin that can be used purposefully as a weapon in bioterrorism ...
,
stress Stress may refer to: Science and medicine * Stress (biology), an organism's response to a stressor such as an environmental condition * Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...
, or
chemicals A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., wit ...
to
mortality Mortality is the state of being mortal, or susceptible to death; the opposite of immortality. Mortality may also refer to: * Fish mortality, a parameter used in fisheries population dynamics to account for the loss of fish in a fish stock throug ...
or
morbidity A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medical conditions that a ...
. The identification of causal relationships between these exposures and outcomes is an important aspect of epidemiology. Modern epidemiologists use
informatics Informatics is the study of computational systems, especially those for data storage and retrieval. According to ACM ''Europe and'' ''Informatics Europe'', informatics is synonymous with computer science and computing as a profession, in which ...
as a tool. Observational studies have two components, descriptive and analytical. Descriptive observations pertain to the "who, what, where and when of health-related state occurrence". However, analytical observations deal more with the 'how' of a health-related event.
Experimental epidemiology An experiment is a procedure carried out to support or refute a hypothesis, or determine the efficacy or likelihood of something previously untried. Experiments provide insight into cause-and-effect by demonstrating what outcome occurs when a ...
contains three case types: randomized controlled trials (often used for a new medicine or drug testing), field trials (conducted on those at a high risk of contracting a disease), and community trials (research on social originating diseases). The term 'epidemiologic triad' is used to describe the intersection of ''Host'', ''Agent'', and ''Environment'' in analyzing an outbreak.


Case series

Case-series may refer to the qualitative study of the experience of a single patient, or small group of patients with a similar diagnosis, or to a statistical factor with the potential to produce illness with periods when they are unexposed. The former type of study is purely descriptive and cannot be used to make inferences about the general population of patients with that disease. These types of studies, in which an astute clinician identifies an unusual feature of a disease or a patient's history, may lead to a formulation of a new hypothesis. Using the data from the series, analytic studies could be done to investigate possible causal factors. These can include case-control studies or prospective studies. A case-control study would involve matching comparable controls without the disease to the cases in the series. A prospective study would involve following the case series over time to evaluate the disease's natural history. The latter type, more formally described as self-controlled case-series studies, divide individual patient follow-up time into exposed and unexposed periods and use fixed-effects Poisson regression processes to compare the incidence rate of a given outcome between exposed and unexposed periods. This technique has been extensively used in the study of adverse reactions to vaccination and has been shown in some circumstances to provide statistical power comparable to that available in cohort studies.


Case-control studies

Case-control studies select subjects based on their disease status. It is a retrospective study. A group of individuals that are disease positive (the "case" group) is compared with a group of disease negative individuals (the "control" group). The control group should ideally come from the same population that gave rise to the cases. The case-control study looks back through time at potential exposures that both groups (cases and controls) may have encountered. A 2×2 table is constructed, displaying exposed cases (A), exposed controls (B), unexposed cases (C) and unexposed controls (D). The statistic generated to measure association is the
odds ratio An odds ratio (OR) is a statistic that quantifies the strength of the association between two events, A and B. The odds ratio is defined as the ratio of the odds of A in the presence of B and the odds of A in the absence of B, or equivalently (due ...
(OR), which is the ratio of the odds of exposure in the cases (A/C) to the odds of exposure in the controls (B/D), i.e. OR = (AD/BC). If the OR is significantly greater than 1, then the conclusion is "those with the disease are more likely to have been exposed," whereas if it is close to 1 then the exposure and disease are not likely associated. If the OR is far less than one, then this suggests that the exposure is a protective factor in the causation of the disease. Case-control studies are usually faster and more cost-effective than
cohort studies A cohort study is a particular form of longitudinal study that samples a cohort (a group of people who share a defining characteristic, typically those who experienced a common event in a selected period, such as birth or graduation), performing ...
but are sensitive to bias (such as
recall bias Recall may refer to: * Recall (bugle call), a signal to stop * Recall (information retrieval), a statistical measure * ''ReCALL'' (journal), an academic journal about computer-assisted language learning * Recall (memory) * ''Recall'' (Overwatc ...
and
selection bias Selection bias is the bias introduced by the selection of individuals, groups, or data for analysis in such a way that proper randomization is not achieved, thereby failing to ensure that the sample obtained is representative of the population int ...
). The main challenge is to identify the appropriate control group; the distribution of exposure among the control group should be representative of the distribution in the population that gave rise to the cases. This can be achieved by drawing a random sample from the original population at risk. This has as a consequence that the control group can contain people with the disease under study when the disease has a high attack rate in a population. A major drawback for case control studies is that, in order to be considered to be statistically significant, the minimum number of cases required at the 95% confidence interval is related to the odds ratio by the equation: :\text = A+C = 1.96^2 (1+N) \left(\frac\right)^2 \left(\frac\right) \approx 15.5 (1+N) \left(\frac\right)^2 where N is the ratio of cases to controls. As the odds ratio approaches 1, the number of cases required for statistical significance grows towards infinity; rendering case-control studies all but useless for low odds ratios. For instance, for an odds ratio of 1.5 and cases = controls, the table shown above would look like this: For an odds ratio of 1.1:


Cohort studies

Cohort studies A cohort study is a particular form of longitudinal study that samples a cohort (a group of people who share a defining characteristic, typically those who experienced a common event in a selected period, such as birth or graduation), performing ...
select subjects based on their exposure status. The study subjects should be at risk of the outcome under investigation at the beginning of the cohort study; this usually means that they should be disease free when the cohort study starts. The cohort is followed through time to assess their later outcome status. An example of a cohort study would be the investigation of a cohort of smokers and non-smokers over time to estimate the incidence of lung cancer. The same 2×2 table is constructed as with the case control study. However, the point estimate generated is the
relative risk The relative risk (RR) or risk ratio is the ratio of the probability of an outcome in an exposed group to the probability of an outcome in an unexposed group. Together with risk difference and odds ratio, relative risk measures the association bet ...
(RR), which is the probability of disease for a person in the exposed group, ''P''e = ''A'' / (''A'' + ''B'') over the probability of disease for a person in the unexposed group, ''P''''u'' = ''C'' / (''C'' + ''D''), i.e. ''RR'' = ''P''e / ''P''u. As with the OR, a RR greater than 1 shows association, where the conclusion can be read "those with the exposure were more likely to develop the disease." Prospective studies have many benefits over case control studies. The RR is a more powerful effect measure than the OR, as the OR is just an estimation of the RR, since true incidence cannot be calculated in a case control study where subjects are selected based on disease status. Temporality can be established in a prospective study, and confounders are more easily controlled for. However, they are more costly, and there is a greater chance of losing subjects to follow-up based on the long time period over which the cohort is followed. Cohort studies also are limited by the same equation for number of cases as for cohort studies, but, if the base incidence rate in the study population is very low, the number of cases required is reduced by .


Causal inference

Although epidemiology is sometimes viewed as a collection of statistical tools used to elucidate the associations of exposures to health outcomes, a deeper understanding of this science is that of discovering ''causal'' relationships. "
Correlation does not imply causation The phrase "correlation does not imply causation" refers to the inability to legitimately deduce a cause-and-effect relationship between two events or variables solely on the basis of an observed association or correlation between them. The id ...
" is a common theme for much of the epidemiological literature. For epidemiologists, the key is in the term
inference Inferences are steps in reasoning, moving from premises to logical consequences; etymologically, the word '' infer'' means to "carry forward". Inference is theoretically traditionally divided into deduction and induction, a distinction that in ...
. Correlation, or at least association between two variables, is a necessary but not sufficient criterion for the inference that one variable causes the other. Epidemiologists use gathered data and a broad range of biomedical and psychosocial theories in an iterative way to generate or expand theory, to test hypotheses, and to make educated, informed assertions about which relationships are causal, and about exactly how they are causal. Epidemiologists emphasize that the "one cause – one effect" understanding is a simplistic mis-belief. Most outcomes, whether disease or death, are caused by a chain or web consisting of many component causes. Causes can be distinguished as necessary, sufficient or probabilistic conditions. If a necessary condition can be identified and controlled (e.g., antibodies to a disease agent, energy in an injury), the harmful outcome can be avoided (Robertson, 2015). One tool regularly used to conceptualize the multicausality associated with disease is the
causal pie model In the field of epidemiology, the causal mechanisms responsible for diseases A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to ...
.


Bradford Hill criteria

In 1965,
Austin Bradford Hill Sir Austin Bradford Hill (8 July 1897 – 18 April 1991) was an English epidemiologist and statistician, pioneered the randomised clinical trial and, together with Richard Doll, demonstrated the connection between cigarette smoking and lung c ...
proposed a series of considerations to help assess evidence of causation, which have come to be commonly known as the "
Bradford Hill criteria The Bradford Hill criteria, otherwise known as Hill's criteria for causation, are a group of nine principles that can be useful in establishing epidemiologic evidence of a causal relationship between a presumed cause and an observed effect and have ...
". In contrast to the explicit intentions of their author, Hill's considerations are now sometimes taught as a checklist to be implemented for assessing causality. Hill himself said "None of my nine viewpoints can bring indisputable evidence for or against the cause-and-effect hypothesis and none can be required ''sine qua non''." # Strength of Association: A small association does not mean that there is not a causal effect, though the larger the association, the more likely that it is causal. # Consistency of Data: Consistent findings observed by different persons in different places with different samples strengthens the likelihood of an effect. # Specificity: Causation is likely if a very specific population at a specific site and disease with no other likely explanation. The more specific an association between a factor and an effect is, the bigger the probability of a causal relationship. # Temporality: The effect has to occur after the cause (and if there is an expected delay between the cause and expected effect, then the effect must occur after that delay). # Biological gradient: Greater exposure should generally lead to greater incidence of the effect. However, in some cases, the mere presence of the factor can trigger the effect. In other cases, an inverse proportion is observed: greater exposure leads to lower incidence. # Plausibility: A plausible mechanism between cause and effect is helpful (but Hill noted that knowledge of the mechanism is limited by current knowledge). # Coherence: Coherence between epidemiological and laboratory findings increases the likelihood of an effect. However, Hill noted that "... lack of such aboratoryevidence cannot nullify the epidemiological effect on associations". # Experiment: "Occasionally it is possible to appeal to experimental evidence". # Analogy: The effect of similar factors may be considered.


Legal interpretation

Epidemiological studies Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in a defined population. It is a cornerstone of public health, and shapes policy decisions and evidenc ...
can only go to prove that an agent could have caused, but not that it did cause, an effect in any particular case: In United States law, epidemiology alone cannot prove that a causal association does not exist in general. Conversely, it can be (and is in some circumstances) taken by US courts, in an individual case, to justify an inference that a causal association does exist, based upon a balance of
probability Probability is the branch of mathematics concerning numerical descriptions of how likely an Event (probability theory), event is to occur, or how likely it is that a proposition is true. The probability of an event is a number between 0 and ...
. The subdiscipline of forensic epidemiology is directed at the investigation of specific causation of disease or injury in individuals or groups of individuals in instances in which causation is disputed or is unclear, for presentation in legal settings.


Population-based health management

Epidemiological practice and the results of epidemiological analysis make a significant contribution to emerging population-based health management frameworks. Population-based health management encompasses the ability to: * Assess the health states and health needs of a target population; * Implement and evaluate interventions that are designed to improve the health of that population; and * Efficiently and effectively provide care for members of that population in a way that is consistent with the community's cultural, policy and health resource values. Modern population-based health management is complex, requiring a multiple set of skills (medical, political, technological, mathematical, etc.) of which epidemiological practice and analysis is a core component, that is unified with management science to provide efficient and effective health care and health guidance to a population. This task requires the forward-looking ability of modern risk management approaches that transform health risk factors, incidence, prevalence and mortality statistics (derived from epidemiological analysis) into management metrics that not only guide how a health system responds to current population health issues but also how a health system can be managed to better respond to future potential population health issues. Examples of organizations that use population-based health management that leverage the work and results of epidemiological practice include Canadian Strategy for Cancer Control, Health Canada Tobacco Control Programs, Rick Hansen Foundation, Canadian Tobacco Control Research Initiative. Each of these organizations uses a population-based health management framework called Life at Risk that combines epidemiological quantitative analysis with demographics, health agency operational research and economics to perform: * ''Population Life Impacts Simulations'': Measurement of the future potential impact of disease upon the population with respect to new disease cases, prevalence, premature death as well as potential years of life lost from disability and death; * ''Labour Force Life Impacts Simulations'': Measurement of the future potential impact of disease upon the labour force with respect to new disease cases, prevalence, premature death and potential years of life lost from disability and death; * ''Economic Impacts of Disease Simulations'': Measurement of the future potential impact of disease upon private sector disposable income impacts (wages, corporate profits, private health care costs) and public sector disposable income impacts (personal income tax, corporate income tax, consumption taxes,
publicly funded health care Publicly funded healthcare is a form of health care financing designed to meet the cost of all or most healthcare needs from a publicly managed fund. Usually this is under some form of democratic accountability, the right of access to which are se ...
costs).


Applied field epidemiology

Applied epidemiology is the practice of using epidemiological methods to protect or improve the health of a population. Applied field epidemiology can include investigating communicable and non-communicable disease outbreaks, mortality and morbidity rates, and nutritional status, among other indicators of health, with the purpose of communicating the results to those who can implement appropriate policies or disease control measures.


Humanitarian context

As the surveillance and reporting of diseases and other health factors become increasingly difficult in humanitarian crisis situations, the methodologies used to report the data are compromised. One study found that less than half (42.4%) of nutrition surveys sampled from humanitarian contexts correctly calculated the prevalence of malnutrition and only one-third (35.3%) of the surveys met the criteria for quality. Among the mortality surveys, only 3.2% met the criteria for quality. As nutritional status and mortality rates help indicate the severity of a crisis, the tracking and reporting of these health factors is crucial. Vital registries are usually the most effective ways to collect data, but in humanitarian contexts these registries can be non-existent, unreliable, or inaccessible. As such, mortality is often inaccurately measured using either prospective demographic surveillance or retrospective mortality surveys. Prospective demographic surveillance requires much manpower and is difficult to implement in a spread-out population. Retrospective mortality surveys are prone to selection and reporting biases. Other methods are being developed, but are not common practice yet.


Validity: precision and bias

Different fields in epidemiology have different levels of validity. One way to assess the validity of findings is the ratio of false-positives (claimed effects that are not correct) to false-negatives (studies which fail to support a true effect). To take the field of genetic epidemiology, candidate-gene studies produced over 100 false-positive findings for each false-negative. By contrast genome-wide association appear close to the reverse, with only one false positive for every 100 or more false-negatives. This ratio has improved over time in genetic epidemiology as the field has adopted stringent criteria. By contrast, other epidemiological fields have not required such rigorous reporting and are much less reliable as a result.


Random error

Random error is the result of fluctuations around a true value because of sampling variability. Random error is just that: random. It can occur during data collection, coding, transfer, or analysis. Examples of random errors include poorly worded questions, a misunderstanding in interpreting an individual answer from a particular respondent, or a typographical error during coding. Random error affects measurement in a transient, inconsistent manner and it is impossible to correct for random error. There is a random error in all sampling procedures. This is called
sampling error In statistics, sampling errors are incurred when the statistical characteristics of a population are estimated from a subset, or sample, of that population. Since the sample does not include all members of the population, statistics of the sample ( ...
. Precision in epidemiological variables is a measure of random error. Precision is also inversely related to random error, so that to reduce random error is to increase precision. Confidence intervals are computed to demonstrate the precision of relative risk estimates. The narrower the confidence interval, the more precise the relative risk estimate. There are two basic ways to reduce random error in an epidemiological study. The first is to increase the sample size of the study. In other words, add more subjects to your study. The second is to reduce the variability in measurement in the study. This might be accomplished by using a more precise measuring device or by increasing the number of measurements. Note, that if sample size or number of measurements are increased, or a more precise measuring tool is purchased, the costs of the study are usually increased. There is usually an uneasy balance between the need for adequate precision and the practical issue of study cost.


Systematic error

A systematic error or bias occurs when there is a difference between the true value (in the population) and the observed value (in the study) from any cause other than sampling variability. An example of systematic error is if, unknown to you, the
pulse oximeter Pulse oximetry is a noninvasive method for monitoring a person's oxygen saturation. Peripheral oxygen saturation (SpO2) readings are typically within 2% accuracy (within 4% accuracy in 95% of cases) of the more accurate (and invasive) reading of ...
you are using is set incorrectly and adds two points to the true value each time a measurement is taken. The measuring device could be precise but not accurate. Because the error happens in every instance, it is systematic. Conclusions you draw based on that data will still be incorrect. But the error can be reproduced in the future (e.g., by using the same mis-set instrument). A mistake in coding that affects ''all'' responses for that particular question is another example of a systematic error. The validity of a study is dependent on the degree of systematic error. Validity is usually separated into two components: *
Internal validity Internal validity is the extent to which a piece of evidence supports a claim about cause and effect, within the context of a particular study. It is one of the most important properties of scientific studies and is an important concept in reason ...
is dependent on the amount of error in measurements, including exposure, disease, and the associations between these variables. Good internal validity implies a lack of error in measurement and suggests that inferences may be drawn at least as they pertain to the subjects under study. *
External validity External validity is the validity of applying the conclusions of a scientific study outside the context of that study. In other words, it is the extent to which the results of a study can be generalized to and across other situations, people, stim ...
pertains to the process of generalizing the findings of the study to the population from which the sample was drawn (or even beyond that population to a more universal statement). This requires an understanding of which conditions are relevant (or irrelevant) to the generalization. Internal validity is clearly a prerequisite for external validity.


Selection bias

Selection bias Selection bias is the bias introduced by the selection of individuals, groups, or data for analysis in such a way that proper randomization is not achieved, thereby failing to ensure that the sample obtained is representative of the population int ...
occurs when study subjects are selected or become part of the study as a result of a third, unmeasured variable which is associated with both the exposure and outcome of interest. For instance, it has repeatedly been noted that cigarette smokers and non smokers tend to differ in their study participation rates. (Sackett D cites the example of Seltzer et al., in which 85% of non smokers and 67% of smokers returned mailed questionnaires.)
24
It is important to note that such a difference in response will not lead to bias if it is not also associated with a systematic difference in outcome between the two response groups.


Information bias

Information bias (epidemiology), Information bias is bias arising from systematic error in the assessment of a variable. An example of this is recall bias. A typical example is again provided by Sackett in his discussion of a study examining the effect of specific exposures on fetal health: "in questioning mothers whose recent pregnancies had ended in fetal death or malformation (cases) and a matched group of mothers whose pregnancies ended normally (controls) it was found that 28% of the former, but only 20% of the latter, reported exposure to drugs which could not be substantiated either in earlier prospective interviews or in other health records". In this example, recall bias probably occurred as a result of women who had had miscarriages having an apparent tendency to better recall and therefore report previous exposures.


Confounding

Confounding In statistics, a confounder (also confounding variable, confounding factor, extraneous determinant or lurking variable) is a variable that influences both the dependent variable and independent variable, causing a spurious association. Con ...
has traditionally been defined as bias arising from the co-occurrence or mixing of effects of extraneous factors, referred to as confounders, with the main effect(s) of interest. A more recent definition of confounding invokes the notion of ''counterfactual'' effects. According to this view, when one observes an outcome of interest, say Y=1 (as opposed to Y=0), in a given population A which is entirely exposed (i.e. exposure ''X'' = 1 for every unit of the population) the risk of this event will be ''R''A1. The counterfactual or unobserved risk ''R''A0 corresponds to the risk which would have been observed if these same individuals had been unexposed (i.e. ''X'' = 0 for every unit of the population). The true effect of exposure therefore is: ''R''A1 − ''R''A0 (if one is interested in risk differences) or ''R''A1/''R''A0 (if one is interested in relative risk). Since the counterfactual risk ''R''A0 is unobservable we approximate it using a second population B and we actually measure the following relations: ''R''A1 − ''R''B0 or ''R''A1/''R''B0. In this situation, confounding occurs when ''R''A0 ≠ ''R''B0. (NB: Example assumes binary outcome and exposure variables.) Some epidemiologists prefer to think of confounding separately from common categorizations of bias since, unlike selection and information bias, confounding stems from real causal effects.


The profession

Few
universities A university () is an institution of higher (or tertiary) education and research which awards academic degrees in several academic disciplines. Universities typically offer both undergraduate and postgraduate programs. In the United States, t ...
have offered epidemiology as a course of study at the undergraduate level. One notable undergraduate program exists at
Johns Hopkins University Johns Hopkins University (Johns Hopkins, Hopkins, or JHU) is a private university, private research university in Baltimore, Maryland. Founded in 1876, Johns Hopkins is the oldest research university in the United States and in the western hem ...
, where students who major in public health can take graduate-level courses, including epidemiology, during their senior year at the
Bloomberg School of Public Health Bloomberg may refer to: People * Daniel J. Bloomberg (1905–1984), audio engineer * Georgina Bloomberg (born 1983), professional equestrian * Michael Bloomberg (born 1942), American businessman and founder of Bloomberg L.P.; politician and m ...
. Although epidemiologic research is conducted by individuals from diverse disciplines, including clinically trained professionals such as physicians, formal training is available through Masters or Doctoral programs including
Master of Public Health The Master of Public Health or Master of Philosophy in Public Health (M.P.H.), Master of Science in Public Health (MSPH), Master of Medical Science in Public Health (MMSPH) and the Doctor of Public Health (Dr.P.H.), International Masters for Healt ...
(MPH),
Master of Science A Master of Science ( la, Magisterii Scientiae; abbreviated MS, M.S., MSc, M.Sc., SM, S.M., ScM or Sc.M.) is a master's degree in the field of science awarded by universities in many countries or a person holding such a degree. In contrast to ...
of Epidemiology (MSc.), Doctor of Public Health (DrPH),
Doctor of Pharmacy A Doctor of Pharmacy (PharmD; New Latin: ''Pharmaciae Doctor'') is a professional doctorate in pharmacy. In some countries, it is a doctoral degree to practice the profession of pharmacy or to become a clinical pharmacist. In many countries the ...
(PharmD),
Doctor of Philosophy A Doctor of Philosophy (PhD, Ph.D., or DPhil; Latin: or ') is the most common Academic degree, degree at the highest academic level awarded following a course of study. PhDs are awarded for programs across the whole breadth of academic fields ...
(PhD),
Doctor of Science Doctor of Science ( la, links=no, Scientiae Doctor), usually abbreviated Sc.D., D.Sc., S.D., or D.S., is an academic research degree awarded in a number of countries throughout the world. In some countries, "Doctor of Science" is the degree used f ...
(ScD). Many other graduate programs, e.g.,
Doctor of Social Work The Doctor of Social Work (DSW) is a professional doctorate in social work, it is the highest academic award available in the field of social work, and most offer advanced training in a professional area of practice including but not limited to; n ...
(DSW), Doctor of Clinical Practice (DClinP),
Doctor of Podiatric Medicine A podiatrist ( ) is a medical professional devoted to the treatment of disorders of the foot, ankle, and related structures of the leg. The term originated in North America but has now become the accepted term in the English-speaking world for ...
(DPM),
Doctor of Veterinary Medicine A veterinarian (vet), also known as a veterinary surgeon or veterinary physician, is a medical professional who practices veterinary medicine. They manage a wide range of health conditions and injuries in non-human animals. Along with this, vet ...
(DVM),
Doctor of Nursing Practice The Doctor of Nursing Practice (DNP) is a professional degree in nursing. In the United States, the DNP is one of three doctorate degrees in nursing, the others being the research degrees PhD and the Doctor of Nursing Science. Internationally, ...
(DNP), Doctor of Physical Therapy (DPT), or for clinically trained physicians,
Doctor of Medicine Doctor of Medicine (abbreviated M.D., from the Latin language, Latin ''Medicinae Doctor'') is a medical degree, the meaning of which varies between different jurisdictions. In the United States, and some other countries, the M.D. denotes a profes ...
(MD) or
Bachelor of Medicine and Surgery Bachelor of Medicine, Bachelor of Surgery ( la, Medicinae Baccalaureus, Baccalaureus Chirurgiae; abbreviated most commonly MBBS), is the primary medical degree awarded by medical schools in countries that follow the tradition of the United Kin ...
(MBBS or MBChB) and
Doctor of Osteopathic Medicine Doctor of Osteopathic Medicine (DO or D.O., or in Australia DO USA) is a medical degree conferred by the 38 osteopathic medical schools in the United States. DO and Doctor of Medicine (MD) degrees are equivalent: a DO graduate may become licens ...
(DO), include some training in epidemiologic research or related topics, but this training is generally substantially less than offered in training programs focused on epidemiology or public health. Reflecting the strong historical tie between epidemiology and medicine, formal training programs may be set in either schools of public health and medical schools. As public health/health protection practitioners, epidemiologists work in a number of different settings. Some epidemiologists work 'in the field'; i.e., in the community, commonly in a public health/health protection service, and are often at the forefront of investigating and combating disease outbreaks. Others work for non-profit organizations, universities, hospitals and larger government entities such as state and local health departments, various Ministries of Health,
Doctors without Borders Doctor or The Doctor may refer to: Personal titles * Doctor (title), the holder of an accredited academic degree * A medical practitioner, including: ** Physician ** Surgeon ** Dentist ** Veterinary physician ** Optometrist *Other roles ** ...
, the
Centers for Disease Control and Prevention The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georgi ...
(CDC), the
Health Protection Agency The Health Protection Agency (HPA) was a non-departmental public body in the United Kingdom. It was an organisation that was set up by the UK government in 2003 to protect the public from threats to their health from infectious diseases and envi ...
, the
World Health Organization The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
(WHO), or the
Public Health Agency of Canada The Public Health Agency of Canada (PHAC; french: Agence de la santé publique du Canada, ASPC) is an agency of the Government of Canada that is responsible for public health, emergency preparedness and response, and infectious and chronic diseas ...
. Epidemiologists can also work in for-profit organizations such as pharmaceutical and medical device companies in groups such as market research or clinical development.


COVID-19

An April 2020
University of Southern California The University of Southern California (USC, SC, or Southern Cal) is a Private university, private research university in Los Angeles, California, United States. Founded in 1880 by Robert M. Widney, it is the oldest private research university in C ...
article noted that "The
coronavirus epidemic The COVID-19 pandemic, also known as the coronavirus pandemic, is an ongoing global pandemic of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The novel virus was first identifie ...
... thrust epidemiology – the study of the incidence, distribution and control of disease in a population – to the forefront of scientific disciplines across the globe and even made temporary celebrities out of some of its practitioners."


See also

* * * * * * * * * * * * * * * * * * * * * * * * * * * *


References


Citations


Sources

* Clayton, David and Michael Hills (1993) ''Statistical Models in Epidemiology'' Oxford University Press. *
Miquel Porta Miquel Porta (Barcelona, 1957) is a Catalan physician, epidemiologist and scholar. He has promoted the integration of biological, clinical and environmental knowledge and methods in health research and teaching, which he has conducted international ...
, editor (2014) "A dictionary of epidemiology", 6th edn, New York: Oxford University Press
A Dictionary of Epidemiology
* Morabia, Alfredo, editor. (2004) A History of Epidemiologic Methods and Concepts. Basel, Birkhauser Verlag. Part I
A History of Epidemiologic Methods and ConceptsA History of Epidemiologic Methods and Concepts
* Smetanin P, Kobak P, Moyer C, Maley O (2005). "The Risk Management of Tobacco Control Research Policy Programs" The World Conference on Tobacco OR Health Conference, 12–15 July 2006, Washington DC. * Szklo M, Nieto FJ (2002). "Epidemiology: beyond the basics", Aspen Publishers. * Robertson LS (2015). Injury Epidemiology: Fourth Edition. Free online at nanlee.net * Rothman K.,
Sander Greenland Sander Greenland (born January 16, 1951) is an American statistician and epidemiologist with many contributions to statistical and epidemiologic methods including Bayesian and causal inference, bias analysis, and meta-analysis. His focus has be ...
, Lash T., editors (2008). "Modern Epidemiology", 3rd Edition, Lippincott Williams & Wilkins.
Olsen J, Christensen K, Murray J, Ekbom A. An Introduction to Epidemiology for Health Professionals. New York: Springer Science+Business Media; 2010


External links


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