A longitudinal study (or longitudinal survey, or panel study) is a
research design
Research design refers to the overall strategy utilized to carry out research that defines a succinct and logical plan to tackle established research question(s) through the collection, interpretation, analysis, and discussion of data.
Incorporat ...
that involves repeated observations of the same variables (e.g., people) over short or long periods of time (i.e., uses
longitudinal data
In statistics and econometrics, panel data and longitudinal data are both multi-dimensional data involving measurements over time. Panel data is a subset of longitudinal data where observations are for the same subjects each time.
Time series and ...
). It is often a type of
observational study
In fields such as epidemiology, social sciences, psychology and statistics, an observational study draws inferences from a sample to a population where the independent variable is not under the control of the researcher because of ethical concer ...
, although it can also be structured as longitudinal
randomized experiment
In science, randomized experiments are the experiments that allow the greatest reliability and validity of statistical estimates of treatment effects. Randomization-based inference is especially important in experimental design and in survey samp ...
.
Longitudinal studies are often used in social-personality and
clinical psychology
Clinical psychology is an integration of social science, theory, and clinical knowledge for the purpose of understanding, preventing, and relieving psychologically based distress or dysfunction and to promote subjective well-being and persona ...
, to study rapid fluctuations in behaviors, thoughts, and emotions from moment to moment or day to day; in
developmental psychology
Developmental psychology is the scientific study of how and why humans grow, change, and adapt across the course of their lives. Originally concerned with infants and children, the field has expanded to include adolescence, adult developme ...
, to study developmental trends across the life span; and in
sociology
Sociology is a social science that focuses on society, human social behavior, patterns of social relationships, social interaction, and aspects of culture associated with everyday life. It uses various methods of empirical investigation an ...
, to study life events throughout lifetimes or generations; and in
consumer research
Marketing research is the systematic gathering, recording, and analysis of qualitative and quantitative data about issues relating to marketing products and services. The goal is to identify and assess how changing elements of the marketing mix ...
and
political polling to study consumer trends. The reason for this is that, unlike
cross-sectional studies
In medical research, social science, and biology, a cross-sectional study (also known as a cross-sectional analysis, transverse study, prevalence study) is a type of observational study that analyzes data from a population, or a representative su ...
, in which different individuals with the same characteristics are compared, longitudinal studies track the same people, and so the differences observed in those people are less likely to be the result of cultural differences across generations, that is, the
cohort effect. Longitudinal studies thus make observing changes more accurate and are applied in various other fields. In medicine, the design is used to uncover predictors of certain diseases. In advertising, the design is used to identify the changes that advertising has produced in the attitudes and behaviors of those within the target audience who have seen the advertising campaign. Longitudinal studies allow
social scientists to distinguish short from long-term phenomena, such as
poverty
Poverty is the state of having few material possessions or little income. Poverty can have diverse . If the poverty rate is 10% at a point in time, this may mean that 10% of the population are always poor or that the whole population experiences poverty for 10% of the time.
Longitudinal studies can be
retrospective
A retrospective (from Latin ''retrospectare'', "look back"), generally, is a look back at events that took place, or works that were produced, in the past. As a noun, ''retrospective'' has specific meanings in medicine, software development, popu ...
(looking back in time, thus using existing data such as medical records or claims database) or
prospective (requiring the collection of new data).
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 ...
are one type of longitudinal study which sample a
cohort
Cohort or cohortes may refer to:
* Cohort (educational group), a group of students working together through the same academic curriculum
* Cohort (floating point), a set of different encodings of the same numerical value
* Cohort (military unit) ...
(a group of people who share a defining characteristic, typically who experienced a common event in a selected period, such as birth or graduation) and perform
cross-section
Cross section may refer to:
* Cross section (geometry)
** Cross-sectional views in architecture & engineering 3D
*Cross section (geology)
* Cross section (electronics)
* Radar cross section, measure of detectability
* Cross section (physics)
**Abs ...
observations at intervals through time. However, not all longitudinal studies are cohort studies, as longitudinal studies can instead include a group of people who do not share a common event.
Advantages
When longitudinal studies are
observational, in the sense that they observe the state of the world without manipulating it, it has been argued that they may have less power to detect
causal relationships than
experiment
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 whe ...
s. However, because of the repeated observation at the individual level, they have more power than cross-sectional observational studies, by virtue of being able to exclude time-invariant unobserved individual differences and also of observing the temporal order of events.
Longitudinal studies do not require large numbers of participants (as in the examples below). Qualitative longitudinal studies may include only a handful of participants, and longitudinal pilot or feasibility studies often have fewer than 100 participants.
Disadvantages
Some of the disadvantages of longitudinal study are that they are time-consuming and expensive. Therefore, they are not convenient.
Longitudinal studies cannot avoid attrition effect, that is, subjects cannot continue to participate in the study for various reasons. Under longitudinal research methods, the loss of the research sample will bias the remaining small sample. Practice effect is also one of the problems. Longitudinal studies tend to be biased by the fact that subjects repeat the same procedure many times, and their performance will be improved or decreased.
Examples
See also
*
Cross-sectional study
*
Time series
In mathematics, a time series is a series of data points indexed (or listed or graphed) in time order. Most commonly, a time series is a sequence taken at successive equally spaced points in time. Thus it is a sequence of discrete-time data. Ex ...
*
Repeated measures design
References
External links
ESDS Longitudinal data serviceCentre for Longitudinal StudiesNational Centre for Longitudinal Data
{{Authority control
Research methods
Epidemiological study projects
Statistical data types
Design of experiments
Cohort study methods
Nursing research
Social research