Sampling Procedure
The CAPS household sample was drawn through a two-stage process. First, the 'enumeration areas' (EAs) used for the 1996 Population Census were divided into three strata according to whether the population of each was predominantly African, predominantly coloured or predominantly white. A sample of primary sampling units (PSUs) was selected within each stratum with probability proportional to size. Within each PSU a sample of 25 screener households was drawn. The Overview and Technical Documentation for Waves 1-2-3-4-5 provides a more detailed discussion of the sampling design. Data users should take the stratification and clustering into account for all analyses. Strata and PSUs are identified by the majpop and cluster variables respectively.
Weighting
The public release data include sample weights that should be used to adjust for the sample design. Three sample weights for wave 1 are included in the data, each of which deal with specific issues.
The first of these weights, "weightsd", adjusts for three critical elements of the sample design: 1) the intentional oversampling of African and white households; 2) the intentional differential sampling of households with and without young adult household members; and 3) the addition of secondary households (backyard shacks) into the sample of screener households in the field. This weight is incorporated into the other two sample weights. The second, weighthr, begins from the first weight and adds additional adjustments for unit non-response at the level of PSUs. The third sample weight, weightyr, is an individual young adult weight that adds additional adjustment for individual non-response. This adjustment is made by calculating response rates for each combination of single years of age, sex, and population group (8x2x3=48 cells) using the information provided on the household questionnaire.
In addition to the three sample design weights, the Waves 1-2-3-4-5 public release data sets include additional weights to adjust for individual young adult non-response in Waves 2, 3, 4 and 5. Since Wave 2 is composed of two sub-waves (Waves 2a & 2b) with different modules asked of different sub-samples, there are three Wave 2 attrition weights. The weight w2a_weightyr corresponds to the Wave 2a sub-sample (approximately one-third of the total CAPS Young adult sample), the weight w2b_weightyr corresponds to the Wave 2b sub-sample (approximately two-thirds of the total CAPS Young adult sample), and the weight w2y_weightyr corresponds to the combined "total" Wave 2 sample. All of these weights are individual young adult weights that add an additional adjustment for individual young adult non-response in Wave 2a, 2b or 2 "total" to the weight weightyr, which adjusts for the sample design and Wave 1 non-response.
Similarly the weights, w3y_weightyr, w4y_weightyr and w5y_weightyr, are individual young adult weights that add additional adjustment for individual young adult non-response in Waves 3, 4 and 5 to the weight weightyr. The adjustment for Wave 2a, 2b, Wave 2 "total", Wave 3, Wave 4 or Wave 5 young adult non-response is made by estimating separate probit models of the probability the respondent completed a Wave 2a, 2b, either of the Wave 2, Wave 3, Wave 4 or Wave 5 young adult questionnaire. Information given in Wave 1 on age, sex and population group was included in the model. As in the construction of the original weight weightyr, the small number of individuals classified as Indian and other were merged with the Coloured group. From the estimation, the predicted probability was inverted and then capped at the 99% percentile to obtain the non-response adjustment.