Families and Children Study
Sample design and response
The FACS sample was selected from Child Benefit records. The main elements of the methodology used were as follows. The sample was stratified by region, and a rural/urban measure within region. A sample of 150 postcode districts or clusters, from the national total of 2,600 districts, was selected proportionate to the numbers of Child Benefit records in each. An equal number of records identified in each of these postcodes was then selected every nth record starting from a random point within each sector. The programming routine was set to produce 100 families in each of the 150 sectors, to provide a starting sample of 15,000 families with children. This was before any opt-outs or screening, or removal of invalid addresses.
The FACS sample is replenished each year by including samples of new Child Benefit recipients in the selected sampling areas. These comprise new families, and existing families who have moved into the areas. These replace those families whose children become independent, and the inevitable loss of many families when they leave the original sampling points (though attempts are made to include such out-movers within the main panel).
From wave 9 (2007) onwards priority sampling was introduced. All families with at least one of the following characteristics were retained in the sample: included: lone parent families; families with a disabled adult and/or child; families with three or more children; low income families (below 70 per cent of median income); and families with a living absent parent. A sampling fraction was applied to the remaining families.
Calculations of the response rates, design effects and complex sampling
errors are available in the FACS annual reports.