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B The Scottish Household Survey

B.1 Background, and topics covered

B.1.1 The Scottish Household Survey ( SHS) started in February 1999. Its principal purpose is to collect information to inform policy on Transport, Communities and Local Government, but other topics are covered, such as household composition, amenities, employment or unemployment, income, assets and savings, credit and debt, health, disabilities and care, and other topics. The SHS provides the first representative Scottish data on many subjects, such as access to the Internet, daily travel patterns, etc. Annex 1 lists the topics which have been included since the survey started.

B.1.2 The SHS was needed because the existing surveys which cover such topics are often too infrequent, insufficiently detailed, or based on too small samples to provide reliable information for Scotland (or areas within Scotland). For example, prior to 2002, the National Travel Survey's sample included only about 300 Scottish households per year, so it could not provide any information about year to year changes in travel patterns, nor could it show how they vary between different parts of Scotland. The SHS was initially funded for four years: 1999 to 2002 inclusive. Following a competitive tender, the contract for the survey was awarded jointly to two firms (now called TNS System Three and Ipsos MORI). After further competitive tenders, the contract for 2003 to 2006 was awarded to the same two contractors, and the contract for 2007 to 2010 to a consortium of TNS System Three, Ipsos MORI and the Scottish Centre for Social Research.

B.1.3 Where appropriate, the SHS uses the harmonised concepts and questions for government social surveys which have been developed by the Government Statistical Service, to facilitate comparison with the results of other government surveys. However, differences in sampling and survey methods mean that SHS results will differ from those of other surveys. It must also be remembered that the SHS is not designed to produce statistics on (eg) unemployment or income: it collects such information only for selecting the data for particular groups of people (such as the unemployed or the low-paid) for further analysis, or for use as "background" variables when analysing other topics (such as the means of travel or the frequency of driving).

B.2 Sampling arrangements: 1999 to 2006

B.2.1 The SHS is a continuous cross-sectional survey: interviewing takes place all year round. Each year, about 15,500 households across Scotland are interviewed. The SHS is designed so that the interviews from each quarter will provide results which are representative of Scotland as a whole. In addition, the survey design is such that results will be available for each of the larger local authorities annually, and for all 32 Scottish local authorities, regardless of size, over two years. The SHS design therefore involves drawing a sample which will produce about 31,000 household interviews which are spread over two years. The requirement to produce results for every local authority, regardless of size, after two years, means that higher sampling fractions are used for Council areas with small populations, in order to ensure a minimum number of household interviews in each area over the two years. A reweighting process (described later) ensures that the variation in sampling fractions does not make the results unrepresentative of Scotland as a whole. The minimum number of household interviews over the two years is 550 (an "average" Council would have about 1,000 household interviews over the two years), and annual results are available for those Councils for which there are a sufficient number of interviews per year. Of course, the smaller the sample upon which the results for a Council are based, the more carefully they will have to be used, and there might be cases where they do not appear sufficiently reliable to be used.

B.2.2 The SHS is intended to be a survey of private households. For the purposes of the survey, a household is defined as one person or a group of people living in accommodation as their only or main residence and either sharing at least one meal a day or sharing the living accommodation. A student's term-time address is taken as his/her "main residence", in order that he/she is counted where he/she lives for most of the year.

B.2.3 The sample was drawn from the Small User file of the Postcode Address File ( PAF), which is a listing of all active address points maintained by the Post Office. The Small User file excludes addresses at which an average of more than 25 items of post are delivered per day. (Blocks of flats etc, which have several dwellings at the same address, are not excluded from the Small User file: in such cases, the file's Multiple Occupancy Indicator is used to count each dwelling separately for the selection of the sample.) Therefore, people in certain types of accommodation (such as nurses homes, student halls of residence, hostels for the homeless, other communal establishments, mobile homes, and sites for travelling people) will be excluded from the SHS unless the accommodation is listed on the Small User file of the PAF and it represents the sole or main residence of the people concerned. So, the SHS's target population includes some - but not all - students, for example. People living in bed and breakfast accommodation may be included, if it is listed in the Small User file of the PAF and if it is their sole or main residence. Prisons, hospitals and military bases are excluded.

B.2.4 In order that the sample would be representative of each Council's area, the main summary groups of the Scottish MOSAIC geo-demographic indicator were used to define strata within each Council area, and a sample of an appropriate size was then drawn within each stratum within each Council area. Scottish MOSAIC is a neighbourhood classification system developed by Experian. It draws on a large number of Census variables, augmented by some published non-Census information, to distinguish between postcodes in terms of types of housing, housing densities and household characteristics. It uses statistical analysis of variables such as home ownership, car ownership, age, health, employment status and occupation to identify types of neighbourhoods with similar characteristics. All households within a given postcode are regarded as being in the same type of neighbourhood: that to which the postcode as a whole is classified. Further information about MOSAIC can be obtained from Experian (the company's Web site is at www.experian.com).

B.2.5 In the areas of the nine Councils which have the highest population densities, the sample of addresses was drawn at random (within each geo-demographic stratum within each Council) at the start of the two-year period. The resulting addresses were then grouped into batches for allocation as interviewer assignments.

B.2.6 For cost-effectiveness, the design of the sample clustered the interviews in the remaining 23 Councils. Enumeration Districts ( EDs) were used as the Primary Sampling Unit. An ED contains, on average, about 150 households. At the start of the two-year period, EDs were selected at random (within each geo-demographic stratum within each Council) with probabilities proportional to their numbers of addresses (taking account of the Multiple Occupancy Indicator ( MOI) values and the required variation in sampling fractions between Councils). Then, nearer the time that the interviews in an ED are due to take place, addresses within that ED are selected at random, using the current PAF.

B.3 Interviewing, response rates and reweighting

B.3.1 The survey interviews are carried out in respondents' homes using Computer Aided Personal Interviewing ( CAPI). On the basis of figures prepared during the 2005 Quality Review of the SHS, they lasted about 46 minutes, on average. Each interview has two parts. The first part is carried out with the Highest Income Householder (the household reference person - see section A.4) or his/her spouse or partner - it took around 18 minutes, on average. This collects mainly factual information about the composition and characteristics of the household. Some questions are asked in respect of each household member. The second part is with a randomly-chosen adult (aged 16+) member of the household - it lasted roughly 29 minutes, on average. This focuses more on individual attitudes and behaviours. Often, both parts of the interview are with the same person - this is always the case in a single adult household. The use of the two-part approach means that, after reweighting (and assuming that there are no non-response biases), the results from the first part interviews should be representative of Scottish households, and the results from the second part interviews should be representative of Scottish adults.

B.3.2 The response rate for the first part, after taking account of 'deadwood' in the sample of addresses (such as small shops and offices, and properties which have been demolished or are unoccupied), was 69.1% in 2006. Among households which participated, the response rate for the "random adult" part of the interview was 91%.

B.3.3 The data are then reweighted to take account of the unequal probabilities of selection inherent in the sample design: the over-sampling (relative to their numbers of households) of the Councils with smaller populations, in order to obtain a minimum number of interviews in each Council; and the under-sampling (relative to their share of the adult population) of adults living in multi-adult households, because only one "random adult" is interviewed in each household. Comparisons with data from other sources, such as the 2001 Census, the National Travel Survey and the Labour Force Survey, suggested that the reweighted data are broadly representative of the Scottish household population; consequently, no further weighting has been carried out.

B.4 Published results, and anonymised data

B.4.1 From 2003, Scotland's People - the SHS annual report, consists of four volumes, some of which are not published in every year:

• Annual Report - many tables of SHS results.
• Fieldwork Outcomes - information about the targets and achieved outcomes, and data quality.
• Methodology - information about sampling and data collection methods.
• Questionnaire- an edited version of the CAPI questionnaire

These publications are all available on the SHS website (see paragraph B5.3). Printed copies are available from the SHS Team, whose contact details are given in paragraph B5.1.

B.4.2 This bulletin is part of a larger series of Transport statistical bulletins which provide some Transport-related results from the SHS. The others are:

• Transport across Scotland: some Scottish Household Survey results for parts of Scotland, the latest edition was published in January 2006. It provides statistics on the SHS's main topics ( apart from the Travel Diary) for each Council area, and some figures for each Regional Transport Partnership area.
• Scottish Household Survey Travel Diary results, the latest edition of which was published in March 2006. It provides the main results from the Travel Diary, including some figures for each Council area and each Regional Transport Partnership area.

These publications are available from Blackwell's Bookshop, and also on the Scottish Government Transport Statistics website at www.scotland.gov.uk/transtat/latest.

B.4.3 SHS results are also included in other Scottish Government publications, such as Scottish Transport Statistics.

B.4.4 Anonymised copies of the survey data are deposited at the UK Data Archive.

B.5 Enquiries and further information

B.5.1 General enquiries about the SHS should be addressed to the survey's Project Manager:

Tel: 0131 244 8420
Fax: 0131 244 7573
E-mail: shs@scotland.gsi.gov.uk

B.5.2 Enquiries about the statistics in this bulletin should be addressed to:

Frank Dixon

Tel: 0131 244 7254
Fax: 0131 244 7281
E-mail: transtat@scotland.gsi.gov.uk

B.5.3 Further information about the survey can be found on the SHSwebsite at http://www.scotland.gov.uk/shs

This website provides some background to the survey, information about the progress of the survey, and the published results. Copies of the Transport Statistics bulletins can be found on the Transport Statistics website at www.scotland.gov.uk/transtat/latest.

B.5.4 Please use the SHS Web site to register your interest in Population and Household Surveys if you wish to be added to an e-mail mailing list to be kept informed of SHS news and developments. The Project Manager will also, on request, distribute paper copies of information about the survey, and about significant developments when they occur, to people who are unable to access the website.

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