Family Resources Survey 2001-02
Framework for sample selection
The FRS uses a stratified clustered probability sample drawn from the Royal Mail's small user's Postcode Address File (PAF). The small user's PAF is a list of all addresses where less than 50 items of mail are received a day, and is updated twice a year.
The survey selects 1,688 postcode sectors with a probability of selection that is proportional to size. Each sector is known as a Primary Sampling Unit (PSU).
The PSUs are stratified by 27 regions and also by three other variables derived from the 1991 Census of Population. It is anticipated that the 2001 census will be used in drawing the 2004-05 sample. Stratifying ensures that the proportions of the sample falling into each group reflect those of the population.
Within each region the postcode sectors are ranked and grouped into eight equal bands using the proportion of heads of households in socio-economic groups one to five or 13. Within each of these eight bands, the PSUs are ranked by the adult economic activity rate and formed into two further bands, resulting in 16 bands for each region. These are then ranked according to the proportion of unemployed men. This set of stratifiers is chosen to have a maximum effectiveness on the accuracy of two key variables: household income and housing costs. The table below summarises the stratifiers.
| Regions |
19 in England (Metropolitan/non-Metropolitan/4 in London) 2 in Wales 6 in Scotland |
| Socio-economic groups |
1 Employers/Managers in large establishments 2 Employers/Managers in small establishments 3 Professional workers (self employed) 4 Professional workers (employees) 5 Non-manual ancillary workers, foremen and supervisors 13 Farmers (employers and managers) |
| Economic activity rate | |
| Male unemployment rate |
Within each PSU a sample of addresses is selected. In 2001-02, 25 addresses were selected per PSU. This means that nationally there was approximately a one in 600 chance of an address being selected.
Each year, one half of the PSUs are retained from the previous year's sample, but with new addresses chosen; for the other half of the sample, a fresh selection of PSUs is made (which in turn will be retained for the following year). This is to improve comparability between years. Further details of the survey process from sample design to delivery of data to the Department for Work and Pensions (DWP) is available in the FRS Technical Report. 
