1. Overview of Census Evaluation and Selected Methods Pres. 2

2. Why evaluate ?
Because the census is a huge operation (size, number of persons involved) prone to errors
To provide users with some measures of quality of census data to help them interpret the results
To identify types and sources of error in order to assist the planning of future censuses
To serve as a basis for constructing a best estimate of census aggregates, such as total population, or to provide adjustment of census results
But…not to criticize the census takers !! 2 2

3. What errors in a census? Coverage errors: Content errors:
Errors in the count of persons or housing units resulting from cases having been “missed” or counted erroneously
Content errors:
Errors in the recorded characteristics of persons or housing units enumerated in the census (e.g. wrong age...) 3

4. Coverage errors Omissions
Missing housing units, households and/or persons during census enumeration
If the whole housing unit is missed, all households and persons living in the housing unit will also be missed
Major causes of omissions are: failure to cover whole land area of a country in creating EAs;
Mistakes made by enumerators in canvassing assigned areas
Ambiguous definitions of EAs, unclear boundaries of EAs, faulty maps or coverage error during the pre-census listing exercise 4 4

5. Coverage errors Omissions contd.
In addition, omissions within EAs can result because all or some of the members of the household were not present at the time of enumeration
Proxy respondents can inadvertently or deliberately omit some members of a household 5

6. Coverage errors Duplications
Occur when persons, households or housing units are counted more than once
Reasons for duplications include:
Overlapping of enumerator’s assignments owing to errors done during pre-census listing and delineation
Failure by enumerators to clearly identify boundaries
In practice, the number of omissions usually exceeds the number of duplicates (net under-counts) 6

7. Coverage errors Erroneous Inclusions This includes:
Housing units, households and persons enumerated while they should have not been (e.g. babies born after the census reference date)
Or enumerated in a wrong place 7

8. Coverage errors Gross error
This is the sum of duplications, erroneous inclusions and omissions
Net error
This is the difference between over-counts and under-counts
Net census under-count exists when number of omissions exceeds the number of duplicates and erroneous enumerations
Net census over-count is the converse 8

9. Methods for evaluation of census errors
Single Source of Data
Demographic analysis of the census
Interpenetration studies
Multiple Sources of Data
Non-matching studies
Demographic analysis using previous censuses
Comparison with administrative sources or existing surveys
Matching studies
Post Enumeration Surveys
Record checks 9 9

10. Single Source of Data Demographic Analysis of the Census
Average number of persons per household
Sex- and age- ratios
Tabulations...
For an overall assessment of quality:
an age pyramid is a standard method
stable population analysis can be undertaken as long as assumptions pertaining to constant fertility and mortality and no migration are met, for countries with declining mortality a quasi-stable model may be appropriate 10

11. Single Source of Data Interpenetrating studies
Method involves drawing subsamples, selected in an identical manner, from the census frame
Each subsample should be capable of providing valid estimates of population parameters
Assignment of personnel (i.e. enumerators, coders, data entry staff, etc.) is done randomly
The method helps to provide an appraisal of the quality of census information and procedures 11 11

12. Multiple Sources of Data – Non matching studies
Demographic Analysis
Results from a census may be compared with data from other demographic systems such as vital registration systems
For example, the cohort component method of demographic analysis uses successive censuses including
life-table survival rates
age-specific rates
age-specific fertility rates and
estimates of international migration 12

13. Multiple Sources of Data – Non matching studies
Demographic Analysis contd.
Population can be projected forward to the reference date of the second census based on estimated levels of and age schedules of fertility, mortality
The expected population is then compared to the enumerated population in the current census
Yet another method is the comparison of age distributions of successive censuses 13

14. Multiple Sources of Data – Non matching studies
Demographic Analysis contd.
Also the cohort survival method which is a regression method can be used, thus, population counts by age from two censuses and deaths by age during the inter-censal period are used to estimate coverage rate 14

15. Multiple Sources of Data – Non matching studies
Comparison with existing household surveys
In theory any probability sample of households or persons can be used to evaluate coverage and content error in a census if:
They have identical items with same concepts and definitions
They are independent from the census
Must have been conducted close to the census date
There should be sufficient identification information to facilitate accurate matching 15 15

16. Multiple Sources of Data – Matching studies
Record checks
Census records are matched with a sample of records from identification systems such as the vital registration system
The relevant respondents to the census questionnaire are traced to the time synchronized with the census
Sources include:
Previous census
Birth registrations
School enrolment
Citizen registration card
Immigration registers etc. 16

17. Multiple Sources of Data – Matching studies
Record checks contd.
Both coverage and content errors could be measured through the above comparisons
To evaluate coverage efficiently the following preconditions are essential:
A large proportion of census population should be covered in record system
The census and record system should be independent from each other
There should be sufficient information in records 17

18. Multiple Sources of Data – Matching studies
To evaluate content efficiently the following preconditions are essential:
The record system should contain some relevant items covered in the census such as age, sex, education, relationship, marital status etc.
Definitions of items should be identical between the census and the record system
Countries that have used record checks include: Demark, Finland, Norway, Sweden, Taiwan and Canada 18

19. Multiple Sources of Data – Matching studies
Post Enumeration Survey (PES)
Consists of two separate coverage studies :
A survey conducted using a sample frame independent of the census. Persons from this survey are matched to the census to estimate the number of persons missed in the census
A survey conducted using a sample drawn from persons enumerated in the census. This sample is re-enumerated to determine if the sample person or unit was erroneously enumerated (inc. erroneously located) 19

20. Multiple Sources of Data – Matching studies
Post Enumeration Survey (PES) contd.
Results can be used to evaluate the reliability of some characteristics such as sex, age, marital status, relationship to reference person or head of the household.
For some countries the results of PES can be used to adjust some census results
Facilitates better interpretation of census results
More discussion of PES is the focus of this workshop 20

21. Strengths and weaknesses of evaluation methods
Single source:
Methods that depend on a single data source provide less insight into the magnitude and types of errors in the census data
The merit is that the methods using such sources do not require additional data to be collected
No need for sophisticated matching although this is also a limitation
They provide a general impression of quality of the census data 21

22. Strengths and weaknesses of evaluation methods (contd.)
Single Source - Interpenetrating studies
Gives good idea of different contribution of component errors to total census error
Helps to identify operational stages that contribute to census error, thus identifying procedural limitations in a census
Demerits include:
That it is an expensive operation demanding many field staff, intensive training and close supervision
Relatively complex in designing and implementation 22

23. Strengths and weaknesses of evaluation methods (contd.)
Multiple sources - Non-matching studies:
Review census results at aggregate rather than unit level i.e. provides only estimates of net census error
Evaluates very limited characteristics such as sex and age distributions
Merit
They are relatively cheap compared to matching studies 23

24. Strengths and weaknesses of evaluation methods (contd.)
Non matching methods - Demographic Analysis:
Advantage – no additional data is needed to be collected to perform the analysis
Less costly
In statistical offices with sufficient numbers of demographers there is no need for additional staff to do the technical analysis
On the negative side these methods provide less insight into the different contributions of component errors to total error in the census
Quality of sources (Vital Statistics…) 24

25. Strengths and weaknesses of evaluation methods (contd.)
Matching methods:
It provide separate estimates of coverage and content error
Prospects of evaluating more characteristics compared to what can be done with non-matching studies
Challenges
Calls for high level technical skills including managerial
Matching is expensive 25

26. Strengths and weaknesses of evaluation methods (contd.)
Post enumeration survey
Merits:
Its results can be used to independently evaluate census coverage and content error, including reliability of selected characteristics collected in a census
Incorporates matching of individuals or units between the census and PES
Its results are generally more reliable than those of the census i.e. it justification for evaluation 26

27. Strengths and weaknesses of evaluation methods (contd.)
Post enumeration survey
Challenges:
Requires highly skilled field and professional staff
Matching is complex
As it is supposed to be carried out immediately after the census at times there is lack of adequate funds to implement the PES exercise 27

28. Thank You!