The findings presented in this book are based on a cross-sectional historical comparison of people at different ages, household types and income levels through a secondary analysis of Family Expenditure Survey of Great Britain (FES) data. (The Office for National Statistics (ONS) conducts the Northern Ireland Family Expenditure Survey, which is very similar to the FES. However, we did not include these data in our analyses). The data were taken from eight years of the FES at five-year intervals over the period 1968-2001. These data were accessed through the Economic and Social Data Service. The FES is a voluntary survey of a random sample of private households in the United Kingdom carried out by the ONS. The FES is primarily a survey of household expenditure on goods and services, as well as household income. The original purpose of the survey was to provide information on spending patterns for the purpose of calculating the Retail Price Index. The survey has been conducted annually since 1957, although since 1994, the survey reference period has changed from the calendar year to the financial year. Data collection is carried out throughout the year to avoid potential bias arising from seasonal variations in expenditures. Respondents maintain a detailed expenditure diary over 14 days to give indicators of their consumption patterns. In addition to expenditure and income data, the FES includes information on a range of socio-economic characteristics of the households (for example, composition, size, social class, occupation and age of the head of household).

The basic unit of the survey is the household, although data are collected at both household and individual level. The FES sample for Great Britain is drawn from the Small Users File of the Postcode Address File. From this, 672 postal sectors in Great Britain are randomly selected during the year after being arranged in strata defined by government office regions (sub-divided into metropolitan and non-metropolitan areas) and two 1991 Census variables – socio-economic group and ownership of cars. The sample size and response rates for each of the years included in these analyses are presented in Table A.1. On average, about 7,000 households are surveyed each year, representing an average response rate of 60%, although this has declined over the period covered in this book.