Post-enumeration Survey (PES) - Statistics South Africa

Statistics South Africa
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2.3.1 Sampling process
The ultimate purpose of the PES was to evaluate the quality of the census data by providing quantitative
information on coverage and content errors. The evaluation focused on the nine (9) provinces in South
Africa, namely Western Cape (WC), Eastern Cape (EC), Northern Cape (NC), Free State (FS), KwaZulu-
Natal (KZN), North West (NW), Gauteng (GP), Mpumalanga (MP) and Limpopo (LP). The initial sampling
frame for the PES was the complete list of Census 2011 enumeration areas (EAs), amounting to
103 576 EAs. However, this frame was reduced to 89 305 EAs after the exclusion of out-of-scope EAs
which amounted to 14 271 EAs (13,8% of all the Census 2011 EAs). It was desired to have included the
workers' hostels in the PES sample, but the current EA type classifications did not single out workers'
hostels. Instead, all institutions, including workers' hostels, etc., were put together to form a type called
'Collective Living Quarters'. Vacant EAs, parks and recreation, industrial, commercial and collective living
quarters were excluded from the PES 2011 frame. The out-of-scope EA types are excluded due to the
difficulty in tracking movers for matching purposes.
The stratification and sampling process was designed to allow for the provision of estimates at national,
provincial, urban and non-urban levels, but estimates will only be reliable at national and provincial
levels.
2.3.2 Stratification
To improve the efficiency of the PES sample design, the sampling frame was divided into homogeneous
strata. For this purpose, variables correlated with coverage error, such as geographic area, were
chosen, since density and accessibility affect the quality of census coverage. In addition, geographic
stratification is necessary to obtain separate estimates by domain of analysis. Therefore, the first level of
stratification corresponded with the geographic domains of estimation defined; namely province and
urban/non-urban zones of residence.
For post-stratification, variables correlated with the extent of coverage, such as subdivisions that were
well delimited and possessed a high degree of internal homogeneity with regard to socio-demographic
characteristics were used. Hence, the sampling frame of EAs was implicitly stratified by geography type:
urban formal, urban informal, tribal area, and rural formal.
2.3.3 Sample size and allocation
A sample of 600 EAs was selected from the total of 89 305 EAs from the Census 2011 EA frame and
was allocated to the provinces based on the PES 2001 standard errors (SEs). The provincial samples
were further allocated to strata using proportional allocation. International best practices recommend a
sample size of 1% of the census EAs should be used for the PES in order to achieve acceptable
precision levels. The budget allocated to the Census 2011 PES could only accommodate a maximum
sample size of 600 EAs. The maximum SE level of 0,025 for the undercount rate was used in order to
obtain a sample size of 600 EAs. This allowed for a reasonable 95% confidence level for the estimate of
Post Enumeration Survey (PES)