The Labour Force Survey sample can be thought of as comprising eight sub-samples (rotation groups), with each sub-sample remaining in the survey for eight months, and one group "rotating out" each month and being replaced by a new group "rotating in". As seven-eighths of the sample are common from one month to the next, changes in the estimates reflect real changes in the labour market, rather than changes in the sample. The replacement sample is generally selected from the same geographic areas as the outgoing one, as part of a representative sampling approach.
The sample comprises three components:
- the matched common sample (people who responded in both the current month and previous month)
- the unmatched common sample (people who responded in the current month but who did not respond in the previous month, or vice versa)
- the incoming rotation group (replacing people who rotated out)
The matched common sample describes the change observed for the same respondents in th current and previous month, while the other two components reflect differences between the aggregate labour force status of different groups of people.
While the rotation groups are designed to be representative of the population, the outgoing and incoming rotation groups will almost always have somewhat different characteristics, as they reflect different households and people. The design of the survey, including the weighting and estimation processes, ensures that these differences are generally relatively minor and do not affect the representativeness of the survey and its estimates. Monthly estimates are designed to be representative, regardless of the relative contribution of the three components of the sample.
The contributions of the three sample components to the original estimates of employed, unemployed and not in the labour force are in the following spreadsheet.