Post Enumeration Surveys in Census
The data collected through any
field inquiry is invariably subject to certain amount of error,
that normally creep in due to the error committed by the investigator
or even the respondent. A massive operation like population census
is no exception. A large number of countries carry out a Post Enumeration
Survey (PES) after the completion of census to systematically measure
the degree of error or in other words the degree of accuracy. The
systematic attempt to estimate the accuracy of the count by sample
surveys has become a part of the census operations in India since
The PES field work for Census
2001, earlier known as Post Enumeration Check, has already been
completed. The main objective of the PES is to quantify the likely
omission or duplication in census enumeration in terms of coverage
of census houses/households or individuals, in other words, to
determine the coverage error. In conducting this survey, opportunity
is also taken to measure error in responses, or the content error
in the recorded household characteristics, with regard to certain
items canvassed in the census.
The PES is usually intended to
provide answer to the questions:
- How accurately the census houses /households/persons
have been enumerated in the census and
- How precisely have certain characteristics
of the household/ individual been recorded in the census.
The PES also serves the important
purpose of providing feedback regarding operational matters like
concepts and procedures, which would help, to some extent, in improving
the future census operations.
In the earlier censuses, the
PES used to be conducted only after the population enumeration.
However, for the first time in Census 2001, in addition to the
usual PES of the population enumeration, a PES of the Houselisting
Operations was also conducted after completion of the Houselisting
Operations.This was carried out in 16 major States (having population
of 10 million and above as per 1991 population census) including
National Capital Territory of Delhi. These 16 states and Delhi
together comprise about 97 percent of the population of the country.
The PES for Houselisting was aimed at measuring the coverage and
content errors to permit better interpretation of data collected
during the Houselisting Operations of Census of India 2001. Thus
two Post Enumeration Surveys have been conducted in the Population
Census 2001, one after the Houselisting Operations in the year
2000 and the other after the Population Enumeration in 2001.
frame and sample selection :
The PES of Houselisting Operations has been conducted
in a sub-sample of the existing Sample Registration System (SRS)
units as a new sampling frame was not available. The SRS units
of the 1991 Census available in the Office of the Registrar General,
India for rural and urban areas separately have been used as
the sampling frame. Wherever, the SRS units had population in
excess of the average size of the Houselisting Blocks (about
650 persons), two or more Houselisting Blocks were carved out
within the SRS units. A sub-sample of the existing SRS units
was selected for the rural and urban areas in each of the States
included for the PES of the Houselisting Operations. A sample
size of 25 percent of the rural SRS units and 50 percent of the
urban SRS units has been selected for the same. The urban SRS
units are divided into city (population more than 0.1 million
or 1 lakh) and non-city (population less than 0.1 million or
1 lakh). The required number of sample units was selected linear
systematically. The objective of the PES Houselisting was to
estimate both the coverage error - (in terms of omission of census
houses) and also content error (housing, household amenities
and asset characteristics).
The PES of the population enumeration
pertaining to the Census of India 2001 was conducted in all the
States and Union territories of the country for the first time.
In earlier censuses, it used to be conducted only in selected States.
In 1991, it was conducted in all the major States having population
of 10 million and above and the states of Himachal Pradesh, Tripura
and Union Territory of Delhi. For the PES of population enumeration-Census
of India 2001, a sample of 3,000 enumeration blocks (EBs) has been
distributed among all the States and Union territories in proportion
to their projected population of 2001 subject to minimum of 100
and 4 EBs for major States and Union territories respectively.
The list of EBs used at the time of the population enumeration
separately for cities, non-city urban and rural areas has been
used as the sampling frame for conducting the PES. For selecting
the sample, the required number of EBs are selected linear systematically
for the above mentioned three areas separately. In the last census,
a second stage sampling was also undertaken by selecting a 10 percent
sub-sample of the residential households enumerated in the census
from each of the selected EBs for the purpose of conducting the
PES. But during the current PES - 2001, all the residential households
in the 3,000 selected EBs are enumerated for estimating the coverage
error. This is an improvement which is expected to greatly enhance
the confidence in the estimation of coverage error. The institutional
and houseless households are excluded from the PES. Due to operational
considerations, the enquiry on content error was limited in nature
and its scope was restricted to few items like age, literacy, marital
status, economic activity and fertility etc.
For the survey on content error,
a 20 percent sub-sample of the 3,000 EBs selected for estimating
the coverage error has been taken linear systematically and all
the residential households in those 20 percent or 600 EBs were
enumerated for that purpose.
PES involves three stages
of operations namely,
(i) independent listing and enumeration
in the selected 3,000 EBs
(ii) desk matching of those with the
census records and
(iii) field reconciliation for those households
or individuals for whom the entries in the two records viz.,
the PES and the census do not match. These are reconciled by
a field visit.