1. Background to the survey
The Scottish Household Survey ( SHS) is a continuous survey of a sample of the general population in private residences in Scotland. The survey started in 1999 and is financed by the Scottish Government. From 1999 to 2006, it was undertaken by a partnership of TNS System Three and Ipsos- MORI Scotland. From 2007 the partnership included the Scottish Centre for Social Research. The aim of the survey is to provide representative information about the composition, characteristics and behaviour of Scottish households, both nationally and at a local authority level.
The survey covers a wide range of topics to allow links to be made between different policy areas. There is a particular focus on informing policy on transport, communities and local government. The survey is carried out over two year sweeps in order to obtain a sample size that is large enough to provide results for individual local authority areas. 2007 is the first year of the 2007/08 sweep.
The purpose of this Headline report is to release the 2007 survey data into the public domain. A full report on the findings of the 2007 survey will be published in August 2008. The figures in this report are provisional and some may be revised slightly for the full annual report.
The survey sample is designed to provide nationally representative samples of private households and of the adult population in private households. This is achieved by splitting the interview between a household respondent and an adult selected at random from the permanent residents of the household.
The current sample design, like the one used from 1999 to 2006, uses a multi-stage stratified design with a mix of unclustered and clustered sampling. In 2007 the sampling strategy was revised to include a higher proportion of unclustered sampling. The requirement for a minimum sample equivalent to a simple random sample of 500 interviews in each local authority area was maintained but the increased efficiency of the survey means that a smaller total sample size is needed to achieve this. As a result of the sampling changes, in 2007, the survey covered 13,414 households and 12,242 random adults. The previous (2006) survey covered 15,618 households and 14,190 random adults.
Interviewing is conducted using Computer Assisted Personal Interviewing ( CAPI). The survey questionnaire is in two parts. The householder or their spouse/partner completes Part 1 of the interview. Once the composition of the household has been established, one of the adults in the household is randomly selected by the computer to complete Part 2. In all households with only one adult the same person completes both parts but as the number of adults in the household increases, the probability of the random adult being the same as the household respondent declines.
The data presented in the report have been weighted in one of two ways. Household data (collected in Part 1 of the interview) are weighted to take account of the disproportionate sampling and response between local authorities. Random adult data (from Part 2) are weighted to reflect both the disproportionate sampling and response to Part 2 between local authorities and the different probabilities of selection within households.
Because of the high level of demand for space in the Scottish Household Survey, a number of sections of the questionnaire are asked of random sub-samples ('streams') of the full SHS sample. Some questions were allocated to streams from the start of the year. Further streaming was undertaken in June 2007 to reduce the length of the questionnaire as it was longer than originally planned. Streamed questions were asked of at least one quarter of the full sample. In this report, where a specific question was asked of a reduced sample size, this is indicated in the relevant table.
The SHS is the source of information on five of the national indicators in the Government's performance framework 1. One of the indicators is derived from information collected in the travel diary and will be reported later this year. This report provides provisional estimates for the remaining four national indicators.
Full details of the SHS can be obtained from the companion Technical Reports of the survey which can be found on-line at http://www.scotland.gov.uk/shs. The change in sample design for this survey year will have had an impact on the design effect of the survey and therefore the confidence intervals of estimates from the survey. Recalculation of the design effects has not been completed ahead of this provisional publication. However, since the aim of the new sample design is to provide estimates with the same degree of precision at lower cost, confidence intervals are unlikely to be very different from those in previous years. The Technical Reports including updated estimates of design effects and guidance on confidence intervals will be published with the main report in August 2008.