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United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan,

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Presentation on theme: "United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan,"— Presentation transcript:

1 United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan, 21-24 November, 2010 Sampling Frames and Sample Design Pres. 5

2 United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan, 21-24 November, 2010 Sample Frames & Sample Design Objectives: Important to define objectives before designing a sample  Items to estimate – coverage error, duplication, omissions, etc.  Geographic level – national, sub-national (province or district, urban/rural, etc.)  Demographic characteristics – sex, age, person, household, etc.  Confidence level  Margin of error

3 United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan, 21-24 November, 2010 Sample Frames & Sample Design Frames: Material from which a sample is drawn  Each unit to be included in the universe  There should be no duplicates  Each unit should be well defined and distinguishable from other units (it should be unique)  Should be updated

4 United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan, 21-24 November, 2010 Sampling Strategies  Probability household surveys  It is usual to make inferences in a PES for a number of analytical domains  Relatively large samples necessary in each domain for reliable estimates  Stratified cluster sample design-common  First-stage units or Primary Sampling Units (PSUs) - many countries use geographically contiguous land areas usually called area clusters or EAs  PPS systematic sample selection  Second-stage, common to canvass all persons in selected households

5 United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan, 21-24 November, 2010 Importance of Stratification  Population subdivided into heterogeneous groups that are internally homogenous  Stratification based on variables correlated with the extent of coverage-geopolitical subdivisions  Internal homogeneity can be maintained with regard to socio-demographic variables e.g. urban stratum  Common strata may include: rural, urban, provinces etc.

6 United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan, 21-24 November, 2010 Multi-stage Cluster Sampling  Usually used when sampling hierarchical populations  The hierarchical levels are called stages  First stage units are called primary sampling units (PSUs) e.g. EAs  Second stage units are called secondary sampling units (SSUs) e.g. households  Last stage units are called ultimate sampling units (USUs) e.g. persons within households which can be selected from EAs

7 United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan, 21-24 November, 2010 Why Area sampling?  At national level only a frame of EAs is required  Data collection is more efficient  Lower costs compared to simple random sampling (SRS)  Supervision is easier  However, estimates are prone to higher variability compared to SRS

8 United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan, 21-24 November, 2010 Choices of PSUs  Must have clearly identifiable and stable boundaries  Must completely cover the relevant population  Preferably must have measures of size  They should be mapped  Must cover the whole country  The number of PSUs must be relatively large

9 United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan, 21-24 November, 2010 Common problems with EAs  Incomplete coverage  Inadequate maps  Poor measures of size or lack of them

10 United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan, 21-24 November, 2010 PES sample design  A single-stage stratified clustered sample design is commonly adopted  When the PSUs i.e. EAs are selected all households in selected EAs are canvassed, or more rarely only a sample (e.g. 1 every 5).  This is beneficial for matching operation

11 United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan, 21-24 November, 2010 Sample Size Sample size depends on estimate requirements  Geographic level (national, province, urban/rural)  Demographic (sex, age)  Reliability  Confidence level

12 United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan, 21-24 November, 2010 Sample Size  To estimate sample size in the case of proportions you must: Know the occurrence of the event in the population by domain of estimation Specify a confidence interval (e.g 95%) Specify the margin of error or precision (e.g 1%)

13 United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan, 21-24 November, 2010 Sample Size (contd.)  To estimate sample size in the case of proportions, the following formula can be used:

14 United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan, 21-24 November, 2010 Sample size (contd.)  From that it is deduced :

15 United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan, 21-24 November, 2010 Sample Size (contd.)  Example: To estimate percentage of households omitted in the census (expected about 5%) ; confidence interval at 95% (t=1.96) for a margin of error of 2 % The sample size works out to be:

16 United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan, 21-24 November, 2010 Sample Size (contd.)  Adjusting for non-response, e.g. 10%:  Adjusting for the design effect for a complex sample design Design effect of 2 is a default value : 2 x 507 =1,014 This may apply to each province (analysis) domains. If they are five provinces Sample size will be 5 x 1,014 = 5,070

17 United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan, 21-24 November, 2010 Sample selection procedures  For greater convenience and efficiency, the sample of PSUs should be selected using a systematic procedure.  If there are good measures of size, probability proportional to size (PPS) should be used to increase the efficiency of the sample design.  Otherwise, the selection should be made with equal probabilities

18 United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan, 21-24 November, 2010 Sample selection procedures -- PPS  1)Order the EAs geographically (and, if applicable, by other stratification characteristic) to allow implicit stratification  2)Record for each EA i of the stratum h the measure of size M hi, typically the number of households or persons from the census mapping operation  3)Cumulate the size measures down the list of EAs, the last cumulated number will be equal to the total number of households (or persons) in stratum h (M h )  4)Determine the number of EAs (n h ) to be selected in a stratum according to the allocation

19 United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan, 21-24 November, 2010 Sample selection procedures –- PPS (contd.)  5)Determine the sampling interval (I h ) by:  6)Obtain a random number (A h ) between 1 and I h inclusively;  7) Determine the selected EAs as follows: S hi =A h + (i-1) x I h, for i = 1,...,n h, rounded up to the next integer  The i-th EA selected will be the one for which the cumulated measure is closest to S hi without exceeding it.

20 United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan, 21-24 November, 2010 Illustration: Selection of Eight EAs with probability Proportional to size

21 United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan, 21-24 November, 2010 Sample Allocation – 2009 Kenyan PES

22 United Nations Workshop on the 2010 World Programme on Population and Housing Censuses: Census Evaluation and Post Enumeration Surveys, Amman, Jordan, 21-24 November, 2010 Thank You!


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