A census is the procedure of systematically acquiring and recording
information about the members of a given population. The term is used
mostly in connection with national population and housing censuses;
other common censuses include agriculture, business, and traffic
United Nations defines the essential features of
population and housing censuses as "individual enumeration,
universality within a defined territory, simultaneity and defined
periodicity", and recommends that population censuses be taken at
least every 10 years.
United Nations recommendations also cover census
topics to be collected, official definitions, classifications and
other useful information to co-ordinate international practice.
The word is of
Latin origin: during the Roman Republic, the census was
a list that kept track of all adult males fit for military service.
The modern census is essential to international comparisons of any
kind of statistics, and censuses collect data on many attributes of a
population, not just how many people there are but now census takes
its place within a system of surveys where it typically began as the
only national demographic data collection. Although population
estimates remain an important function of a census, including exactly
the geographic distribution of the population, statistics can be
produced about combinations of attributes e.g. education by age and
sex in different regions. Current administrative data systems allow
for other approaches to enumeration with the same level of detail but
raise concerns about privacy and the possibility of biasing
A census can be contrasted with sampling in which information is
obtained only from a subset of a population; typically main population
estimates are updated by such intercensal estimates. Modern census
data are commonly used for research, business marketing, and planning,
and as a baseline for designing sample surveys by providing a sampling
frame such as an address register.
Census counts are necessary to
adjust samples to be representative of a population by weighting them
as is common in opinion polling. Similarly, stratification requires
knowledge of the relative sizes of different population strata which
can be derived from census enumerations. In some countries, the census
provides the official counts used to apportion the number of elected
representatives to regions (sometimes controversially – e.g., Utah
v. Evans). In many cases, a carefully chosen random sample can provide
more accurate information than attempts to get a population census.
2 Residence definitions
3 Enumeration strategies
Census and development
6 Uses of census data
Census data and research
8 Historical censuses
8.2 Ancient Greece
8.3 Ancient Israel
8.7 Rashidun and Umayyad Caliphates
8.8 Medieval Europe
8.9 Inca Empire
8.10 Spanish Empire
9 World population estimates
10 Modern implementation
11 See also
14 External links
A census is often construed as the opposite of a sample as its intent
is to count everyone in a population rather than a fraction. However,
population censuses rely on a sampling frame to count the population.
This is the only way to be sure that everyone has been included as
otherwise those not responding would not be followed up on and
individuals could be missed. The fundamental premise of a census is
that the population is not known and a new estimate is to be made by
the analysis of primary data. The use of a sampling frame is
counterintuitive as it suggests that the population size is already
known. However, a census is also used to collect attribute data on the
individuals in the nation. This process of sampling marks the
difference between historical census, which was a house to house
process or the product of an imperial decree, and the modern
statistical project. The sampling frame used by census is almost
always an address register. Thus it is not known if there is anyone
resident or how many people there are in each household. Depending on
the mode of enumeration, a form is sent to the householder, an
enumerator calls, or administrative records for the dwelling are
accessed. As a preliminary to the dispatch of forms, census workers
will check any address problems on the ground. While it may seem
straightforward to use the postal service file for this purpose, this
can be out of date and some dwellings may contain a number of
independent households. A particular problem is what are termed
'communal establishments' which category includes student residences,
religious orders, homes for the elderly, people in prisons etc. As
these are not easily enumerated by a single householder, they are
often treated differently and visited by special teams of census
workers to ensure they are classified appropriately.
Individuals are normally counted within households and information is
typically collected about the household structure and the housing. For
this reason international documents refer to censuses of population
and housing. Normally the census response is made by a household,
indicating details of individuals resident there. An important aspect
of census enumerations is determining which individuals can be counted
from which cannot be counted. Broadly, three definitions can be used:
de facto residence; de jure residence; and, permanent residence. This
is important to consider individuals who have multiple or temporary
addresses. Every person should be identified uniquely as resident in
one place but where they happen to be on
Census Day, their de facto
residence, may not be the best place to count them. Where an
individual uses services may be more useful and this is at their
usual, or de jure, residence. An individual may be represented at a
permanent address, perhaps a family home for students or long term
migrants. It is necessary to have a precise definition of residence to
decide whether visitors to a country should be included in the
population count. This is becoming more important as students travel
abroad for education for a period of several years. Other groups
causing problems of enumeration are new born babies, refugees, people
away on holiday, people moving home around census day, and people
without a fixed address. People having second homes because of working
in another part of the country or retaining a holiday cottage are
difficult to fix at a particular address sometimes causing double
counting or houses being mistakenly identified as vacant. Another
problem is where people use a different address at different times
e.g. students living at their place of education in term time but
returning to a family home during vacations or children whose parents
have separated who effectively have two family homes. Census
enumeration has always been based on finding people where they live as
there is no systematic alternative - any list you could use to find
people is derived from census activities in the first place. Recent UN
guidelines provide recommendation on enumerating such complex
Historical censuses used crude enumeration assuming absolute accuracy.
Modern approaches take into account the problems of overcount and
undercount, and the coherence of census enumerations with other
official sources of data. This reflects a realist approach to
measurement, acknowledging that under any definition of residence
there is a true value of the population but this can never be measured
with complete accuracy. An important aspect of the census process is
to evaluate the quality of the data.
Many countries use a post-enumeration survey to adjust the raw census
counts. This works in a similar manner to capture-recapture
estimation for animal populations. In census circles this method is
called dual system enumeration (DSE). A sample of households are
visited by interviewers who record the details of the household as at
census day. These data are then matched to census records and the
number of people missed can be estimated by considering the number
missed in the census or survey but counted in the other. This way
counts can be adjusted for non-response varying between different
demographic groups. An explanation using a fishing analogy can be
found in "Trout, Catfish and Roach..." which won an award from the
Royal Statistical Society
Royal Statistical Society for excellence in official statistics in
Enumerator conducting a survey using a mobile phone based
questionnaire in rural Zimbabwe.
Triple system enumeration has been proposed as an improvement as it
would allow evaluation of the statistical dependence of pairs of
sources. However, as the matching process is the most difficult aspect
of census estimation this has never been implemented for a national
enumeration. It would also be difficult to identify three different
sources that were sufficiently different to make the triple system
effort worthwhile. The DSE approach has another weakness in that it
assumes there is no person counted twice (over count). In de facto
residence definitions this would not be a problem but in de jure
definitions individuals risk being recorded on more than one form
leading to double counting. A particular problem here are students who
often have a term time and family address.
Several countries have used a system which is known as short form/long
form. This is a sampling strategy which randomly chooses a
proportion of people to send a more detailed questionnaire to (the
long form). Everyone receives the short form questions. Thereby more
data are collected but not imposing a burden on the whole population.
This also reduces the burden on the statistical office. Indeed, in the
UK all residents were required to fill in the whole form but only a
10% sample were coded and analysed in detail, until 2001. New
technology means that all data are now scanned and processed. Recently
there has been controversy in Canada about the cessation of the long
form with the head,
Munir Sheikh resigning.
The use of alternative enumeration strategies is increasing but
these are not so simple as many people assume and only occur in
developed countries. The
Netherlands has been most advanced in
adopting a census using administrative data. This allows a simulated
census to be conducted by linking several different administrative
databases at an agreed time. Data can be matched and an overall
enumeration established accounting for where the different sources are
discrepant. A validation survey is still conducted in a similar way to
the post enumeration survey employed in a traditional census. Other
countries which have a population register use this as a basis for all
the census statistics needed by users. This is most common amongst
Nordic countries but requires a large number of different registers to
be combined including population, housing, employment and education.
These registers are then combined and brought up to the standard of a
statistical register by comparing the data in different sources and
ensuring the quality is sufficient for official statistics to be
produced. A recent innovation is the French instigation of a
rolling census programme with different regions enumerated each year
such that the whole country is completely enumerated every 5 to 10
years. In Europe, in connection with the 2010 census round, a
large number of countries adopted alternative census methodologies,
often based on the combination of data from registers, surveys and
Censuses have evolved in their use of technology with the latest
censuses, the 2010 round, using many new types of computing. In
Brazil, handheld devices were used by enumerators to locate residences
on the ground. In many countries, census returns could be made via the
Internet as well as in paper form. DSE is facilitated by computer
matching techniques which can be automated, such as propensity score
matching. In the UK, all census formats are scanned and stored
electronically before being destroyed, replacing the need for physical
archives. The record linking to perform an administrative census would
not be possible without large databases being stored on computer
New technology is not without problems in its introduction. The US
census had intended to use the handheld computers but cost escalated
and this was abandoned, with the contract being sold to Brazil. Online
response is a good idea but one of the functions of census is to make
sure everyone is counted accurately. A system which allowed people to
enter their address without verification would be open to abuse.
Therefore, households have to be verified on the ground, typically by
an enumerator visit or post out. Paper forms are still necessary for
those without access to Internet connections. It is also possible that
the hidden nature of an administrative census means that users are not
engaged with the importance of contributing their data to official
Alternatively, population estimations may be carried out remotely with
GIS and remote sensing technologies.
Census and development
According to UNFPA, “The information generated by a population and
housing census – numbers of people, their distribution, their living
conditions and other key data – is critical for development.” 
This is because this type of data is essential for policymakers so
that they know where to invest. Unfortunately, many countries have
outdated or inaccurate data about their populations and therefore,
without accurate data are unable to address the needs of their
UNFPA stated that,
“The unique advantage of the census is that it represents the entire
statistical universe, down to the smallest geographical units, of a
country or region. Planners need this information for all kinds of
development work, including: assessing demographic trends; analysing
socio-economic conditions; designing evidence-based
poverty-reduction strategies; monitoring and evaluating the
effectiveness of policies; and tracking progress toward national and
internationally agreed development goals.”
In addition to making policymakers aware about population issues, it
is also an important tool for identifying forms of social, demographic
or economic exclusions, such as inequalities relating to race, ethics
and religion as well as disadvantaged groups such as those with
disabilities and the poor.
An accurate census can empower local communities by providing them
with the necessary information to participate in local decision-making
and ensuring they are represented.
Uses of census data
In the nineteenth century, the first censuses collected paper
enumerations that had to be collated by hand so the statistical uses
were very basic. The government owned the data and were able to
publish statistics themselves on the state of the nation. Uses
were to measure changes in the population and apportion
representation. Population estimates could be compared to those of
By the beginning of the twentieth century, censuses were recording
households and some indications of their employment. In some
countries, census archives are released for public examination after
many decades, allowing genealogists to track the ancestry of
interested people. Archives provide a substantial historical record
which may challenge established notions of tradition. It is also
possible to understand the societal history through job titles and
arrangements for the destitute and sick.
There are a lot of politics that surround the census in many
countries. In Canada in 2010 for example, the government under the
leadership of Stephen Harper abolished the mandatory long-form census.
The decision to cut the long-form census was a response to protests
from some Canadians who resented the personal questions.  The
long-form census was reinstated by the Justin Trudeau government in
Census data and research
As governments assumed responsibility for schooling and welfare, large
government research departments made extensive use of census data.
Actuarial estimates could be made to project populations and plan for
provision in local government and regions. It was also possible for
central government to allocate funding on the basis of census data.
Even into the mid twentieth century, census data was only directly
accessible to large government departments. However, computers meant
that tabulations could be used directly by university researchers,
large businesses and local government offices. They could use the
detail of the data to answer new questions and add to local and
Now, census data are published in a wide variety of formats to be
accessible to business, all levels of governance, media, students and
teachers, charities and any citizen who is interested; researchers in
particular have an interest in the role of
Census Field Officers (CFO)
and their assistants. Data can be represented visually or analysed
in complex statistical models, to show the difference between certain
areas, or to understand the association between different personal
Census data offer a unique insight into small areas
and small demographic groups which sample data would be unable to
capture with precision.
Although the census provides a useful way of obtaining statistical
information about a population, such information can sometimes lead to
abuses, political or otherwise, made possible by the linking of
individuals' identities to anonymous census data. This
consideration is particularly important when individuals' census
responses are made available in microdata form, but even
aggregate-level data can result in privacy breaches when dealing with
small areas and/or rare subpopulations.
For instance, when reporting data from a large city, it might be
appropriate to give the average income for black males aged between 50
and 60. However, doing this for a town that only has two black males
in this age group would be a breach of privacy because either of those
persons, knowing his own income and the reported average, could
determine the other man's income.
Typically, census data are processed to obscure such individual
information. Some agencies do this by intentionally introducing small
statistical errors to prevent the identification of individuals in
marginal populations; others swap variables for similar
respondents. Whatever measures have been taken to reduce the privacy
risk in census data, new technology in the form of better electronic
analysis of data poses increasing challenges to the protection of
sensitive individual information. This is known as statistical
Another possibility is to present survey results by means of
statistical models in the form of a multivariate distribution
mixture. The statistical information in the form of conditional
distributions (histograms) can be derived interactively from the
estimated mixture model without any further access to the original
database. As the final product does not contain any protected
microdata, the model based interactive software can be distributed
without any confidentiality concerns.
Another method is simply to release no data at all, except very large
scale data directly to the central government. Different release
strategies between government have led to an international project
(IPUMS) to co-ordinate access to microdata and corresponding metadata.
Such projects also promote standardising metadata by projects such as
SDMX so that best use can be made of the minimal data available.
Egypt first appears in the late Middle Kingdom and
develops in the New Kingdom Pharaoh Amasis, according to
Herodotus, require every Egyptian to declare annually to the nomarch,
"whence he gained his living". Under the
Ptolemies and the Romans
several censuses were conducted in
Egypt by governments officials 
There are several accounts of ancient Greek city states carrying out
Censuses are mentioned in the Bible. God commands a per capita tax to
be paid with the census in Exodus 30:11-16 for the upkeep of the
Book of Numbers
Book of Numbers is named after the counting of the
Israelite population (in Numbers 1-4) according to the house of the
Fathers after the exodus from Egypt. A second census was taken while
the Israelite were camped in the plains of Moab, in Numbers 26.
David performed a census that produced disastrous results (in 2
Samuel 24 and 1 Chronicles 21). His son, King Solomon, had all of the
foreigners in Israel counted in 2 Chronicles 2:17.
When the Romans took over Judea in AD 6, the legate Publius
Sulpicius Quirinius organised a census for tax purposes. The Gospel of
Luke links the birth of
Jesus to this event. Luke 2.
One of the world's earliest preserved censuses was held in China
in AD 2 during the Han Dynasty, and is still considered by
scholars to be quite accurate. Another census was held
in AD 144.
The oldest recorded census in India is thought to have occurred around
300 BC during the reign of The Emperor
Chandragupta Maurya under
the leadership of
Kautilya or Chanakya and Ashoka.
Roman censor and Indiction
The word "census" originated in ancient Rome from the
censere ("to estimate"). The census played a crucial role in the
administration of the Roman Empire, as it was used to determine taxes.
With few interruptions, it was usually carried out every five
years. It provided a register of citizens and their property from
which their duties and privileges could be listed. It is said to have
been instituted by the Roman king
Servius Tullius in the 6th century
BC, at which time the number of arms-bearing citizens was
supposedly counted at around 80,000. The 6 AD "census of
Quirinius" undertaken following the imposition of direct Roman rule in
Judea was partially responsible for the development of the Zealot
movement and several failed rebellions against Rome that ended in the
Diaspora. The 15-year indiction cycle established by
AD 297 was based on quindecennial censuses and formed the basis
for dating in late antiquity and under the Byzantine Empire.
Rashidun and Umayyad Caliphates
In the Middle Ages, the
Caliphate began conducting regular censuses
soon after its formation, beginning with the one ordered by the second
Rashidun caliph, Umar.
Domesday Book was undertaken in AD 1086 by William I of
England so that he could properly tax the land he had recently
conquered in medieval Europe. In 1183, a census was taken of the
crusader Kingdom of Jerusalem, to ascertain the number of men and
amount of money that could possibly be raised against an invasion by
Saladin, sultan of
Egypt and Syria.
In the 15th century, the
Inca Empire had a unique way to record census
information. The Incas did not have any written language but recorded
information collected during censuses and other numeric information as
well as non-numeric data on quipus, strings from llama or alpaca hair
or cotton cords with numeric and other values encoded by knots in a
base-10 positional system.
On May 25, 1577, King
Philip II of Spain
Philip II of Spain ordered by royal cédula the
preparation of a general description of Spain's holdings in the
Indies. Instructions and a questionnaire, issued in 1577 by the Office
of the Cronista Mayor, were distributed to local officials in the
Viceroyalties of New Spain and Peru to direct the gathering of
information. The questionnaire, composed of fifty items, was designed
to elicit basic information about the nature of the land and the life
of its peoples. The replies, known as "relaciones geográficas," were
written between 1579 and 1585 and were returned to the Cronista Mayor
in Spain by the Council of the Indies.
World population estimates
The earliest estimate of the world population was made by Giovanni
Battista Riccioli in 1661; the next by
Johann Peter Süssmilch
Johann Peter Süssmilch in
1741, revised in 1762; the third by Karl Friedrich Wilhelm Dieterici
In 1931 Walter Willcox published a table in his book, International
Migrations: Volume II Interpretations, that estimated the 1929 world
population to be roughly 1.8 billion.
League of Nations and International Statistical Institute estimates of
the world population in 1929
Main article: Population and housing censuses by country
Nigerian leaders cannot put a number on the amount of Nigerian women
and girls that have gone missing. Nigeria has never had a credible,
successful census. —Olúfémi Táíwò, professor of Africana
studies at Cornell University
Languages in censuses
Race and ethnicity in censuses
United Nations (2008). Principles and Recommendations for Population
and Housing Censuses. Statistical Papers: Series M No. 67/Rev.2. p8.
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troisième et deuxième millénaires" CRIPEL 9 (1987) 37 - 49.
^ Herodotus, Histories II, 177, 2
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^ Scheidel, Walter (2009) Rome and China: comparative perspectives on
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Livy Ab urbe condita 1.42
Livy Ab urbe condita 1.42, citing Fabius Pictor
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Effects of UK 'Jedi' hoax on 2001 UK census from ONS.
Census Press Release on 1930 Census.
Census Press Release on Soundex and WPA.
Wikimedia Commons has media related to Census.
"Census". Encyclopædia Britannica. 5 (11th ed.). 1911.
Census of Ireland 1911.
Online Historical Population Reports Project (OHPR).
PR as a function of census management: comparative analysis of fifteen
Coefficient of variation
Central limit theorem
Index of dispersion
Pearson product-moment correlation
Sample size determination
Method of moments
1- & 2-tails
Uniformly most powerful test
Goodness of fit
Signed rank (Wilcoxon)
Rank sum (Mann–Whitney)
Ordered alternative (Jonckheere–Terpstra)
Maximum posterior estimator
Coefficient of determination
Errors and residuals
Regression model validation
Mixed effects models
Simultaneous equations models
Multivariate adaptive regression splines (MARS)
Simple linear regression
Ordinary least squares
General linear model
Generalized linear model
Logistic (Bernoulli) / Binomial / Poisson regressions
Partition of variance
Analysis of variance
Analysis of variance (ANOVA, anova)
Analysis of covariance
Degrees of freedom
Categorical / Multivariate / Time-series / Survival
Structural equation model
ARIMA model (Box–Jenkins)
Autoregressive conditional heteroskedasticity (ARCH)
Vector autoregression (VAR)
Spectral density estimation
Kaplan–Meier estimator (product limit)
Proportional hazards models
Accelerated failure time (AFT) model
First hitting time
Clinical trials / studies
Process / quality control
Geographic information system
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