Sampling Procedure
The Quarterly Labour Force Survey (QLFS) uses the Master Sample frame that has been developed as a general-purpose household survey frame. The 2013 Master Sample is based on information collected during the 2011 Census. There are 3 324 primary sampling units in the Master Sample, with an expected sample of approximately 33 000 dwelling units. The sampling procedure for the QLFS is based on a stratified two-stage design with probability proportional to size (PPS) sampling of PSUs in the first stage, and sampling of dwelling units (DUs) with systematic sampling in the second stage.
The Master Sample is designed to be representative at the provincial level and within provinces at metro/non-metro levels. The sample is divided equally into four subgroups or panels called rotation groups. For each quarter of the QLFS, a quarter of the sampled dwellings are rotated out of the sample and replaced by new dwellings from the same PSU or the next PSU on the list.
Deviations from the Sample Design
It should be noted that the Quarterly Labour Force Survey (QLFS) for Quarter 1 (January to March) of 2020 data collection was disrupted when Stats SA suspended face-to-face data collection for all its surveys on 19 March 2020 as a result of the COVID-19 pandemic and restricted movement. This was to ensure that the field staff and respondents were not exposed to the risk of contracting coronavirus and to contain its spread. As a result, some dwellings (621 or 2,0% of the 30 608 sampled dwelling units) were not interviewed which otherwise would have been interviewed. To compensate for this, Stats SA made use of the fact that the design of the QLFS is such that sampled dwelling units are in the sample for four successive quarters. So, for persons in dwelling units that were not visited as a result of the lockdown, imputations were done where possible using data from the previous quarter. For respondents who were not visited in the first quarter of 2020 but had information from the fourth quarter of 2019, their responses were carried over to the first quarter of 2020.
If the person was shown as unemployed or not economically active in the last quarter of 2019, that was the status assigned to them for the first quarter of 2020. If the person was shown as employed in the fourth quarter of 2019, the imputation was somewhat more complex. This was necessitated by the fact that that there are usually temporary jobs created in the fourth quarter of each year that do not continue into the following year. Accordingly, if the person started the job that he/she held in Q4: 2019 in some previous quarter, it was assumed that the job continued into Q1: 2020. On the other hand, if the job held in Q4: 2019 had only started in that quarter, that person was treated as non-respondent in Q1: 2020.
