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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 in its three main areas of Transport, Local Government and Social Inclusion, but other topics are covered, such as household composition, housing and amenities, overcrowding and sharing in housing, 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. The Annex lists the topics which were included when 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, the National Travel Survey's sample includes only about 300 Scottish households per year, so it cannot provide any information about year to year changes in travel patterns, nor can it show how they vary between different parts of Scotland. The Scottish Executive will, initially, fund the SHS for four years: 1999 to 2002 inclusive. The contract for the survey was awarded following a competitive tender. The SHS is conducted jointly by two firms: System Three and MORI Scotland.
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
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 ten 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.
B.2.5 In the areas of the ten 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 22 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 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, which lasted an average of 42 minutes in 1999, are carried out in respondents’ homes using Computer Aided Personal Interviewing (CAPI) by System Three and MORI Scotland. The interview has two parts. The first part of the interview is carried out with the Highest Income Householder (the household reference person - see section A.4) or his/her spouse or partner. 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. 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 65% in 1999. However, because the SHS is conducted in two-year "sweeps", addresses which were issued for interview in 1999 remain eligible for interview in 2000, and some of the households which did not respond in 1999 will be interviewed in 2000. Therefore, it is expected that the final response rate will be more than 65% Among households which participated, the response rate for the "random adult" part of the interview was 96%.
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 National Travel Survey and the 1996 Scottish House Condition 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 The following SHS publications are available from The Stationery Office Bookshop, and are also available on the SHS website (see section B.5.3):
B.4.2 SHS results are also included in other Scottish Executive publications, such as "Scottish Transport Statistics no. 1999 / 2000 edition". They will also appear in a number of new Transport statistical bulletins, of which this is the first.
B.4.3 Anonymised copies of each year's data will be deposited at the ESRC 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:
Louise
Finlayson
SHS Project Manager
Central Research Unit
Scottish Executive
Victoria Quay
Edinburgh, EH6
6QQ
Tel: 0131 244 7557
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
Transport Statistician
Scottish
Executive
Victoria Quay
Edinburgh, EH6 6QQ
Tel:
0131 244 7254
Fax: 0131 244 0888
E-mail: frank.dixon@scotland.gsi.gov.uk
B.5.3 Further information about the survey can be found on the SHS website 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.
B.5.4 Please contact the Project Manager if you wish to be added to an e-mail mailing list to be kept informed of any significant updates to the information on the SHS website. 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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