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2. Background
2.1 This bulletin provides information, collected by the Scottish Household Survey ( SHS), about the transport facilities available to private households, and about some travel by household members, for parts of Scotland. The topics covered include: the availability for private use of cars; people's possession of driving licences and their frequency of driving; how car drivers usually make particular types of journey and whether they could use another means of transport; people's frequency of walking and cycling; the accessibility and frequency of bus services; people's views on the convenience of public transport; the frequency of use of local bus and train services; users' views on aspects of local bus services; how safe from crime people felt, or would feel, when travelling in the evening by bus or by train; the usual method of travel to work; whether people work from home; whether car commuters could use public transport; where people who drive to work park; and travel to school. The figures relate to the two-year period 2003/2004 (and, in some cases, to the previous two-year periods 1999/2000 and 2001/2002) because the SHS was designed to provide figures for most local authority areas only for such two-year periods.
2.2 Statistics are provided for each Council area, and for each category of a six-way urban/rural classification which was developed for use in analysing the results of the SHS. In this classification, a "small town" has a population between 3,000 and 9,999 (inclusive), and an area is described as "accessible" if it is within 30 minutes' drive of a settlement with a population of 10,000 or more (otherwise it is described as "remote"). A "large urban area" is a settlement with a population of 125,000 or more. More details of the classification are given in Section 9. Some statistics are also given for the areas of the new Regional Transport Partnerships - please see section A.7 in the "Notes and Definitions".
2.3 The SHS collects a wide range of information. Some questions are asked about the household as a whole, and all the people in it; some relate only to one randomly-chosen adult (aged 16+) member of the household; and some are asked only about one randomly-chosen schoolchild member of the household (if there is one). Some questions are answered on behalf of the household by the Highest Income Householder (please see section A.4 in the "Notes and Definitions") or his/her spouse/partner; others are answered by the randomly-chosen adult on behalf of him/herself. The results are weighted to take account of differences in selection probabilities. The statistics given here were extracted in November 2005, so will not take account of subsequent revisions to the SHS database.
2.4 As with all such surveys, sampling variability and non-response bias may affect the results. It is particularly important to keep this in mind when looking at the results for individual Council areas, because some of them may be affected by quite large percentage sampling errors. In general, the smaller the sample from which an estimate has been produced, the greater the likelihood that the estimate could be misleading. As an example, Table 22 provides information about travel to school. In some cases, the figure for a Council area is based on data for only a hundred or so school pupils, each of whom therefore represents about 1% of the total. So, which particular households were selected for inclusion in the sample could make a significant difference to the results, which are therefore subject to considerable potential sampling variability. For example, the estimate of the percentage of pupils in that Council area who cycle to school would have been two or three percentage points higher had the SHS sample included, purely by chance, just two or three more children who cycled to school. In a "low population density" Council area, the "clustering" of the sample increases the potential sampling variability: for example, the estimated percentage who walk to school could be over-estimated greatly if, by chance, disproportionately many of the "rural" sample clusters chosen were in villages with schools, and disproportionately few were in places far from schools. Hence, an estimate that (say) 50% walk to school, produced from a sample of 100 or so school pupil households, may only indicate that the true value for the area is likely to be between 40% and 60%. Section 10 provides more information on the possible scale of sampling errors.
2.5 There are other reasons why the SHS results may provide only broad indications for some Council areas. First, the non-response rate is particularly high in some Council areas. Should the characteristics of non-respondents differ markedly from those of the people in the survey, the results could be biased. Unfortunately, by its nature, the scale of any non-response bias is very difficult to quantify, as the survey does not collect information about the characteristics of non-respondents. Second, as it is a survey of private households, the SHS does not cover some sections of the population - for example, it does not collect information about many students, such as those who live in halls of residence (see section B.2.3 of the background information about the survey).
2.6 It follows that figures for individual Council areas should be used cautiously, particularly those based on small samples. When comparing the figures for different Council areas, it is particularly important to note that small differences may well be the result of sampling variability rather than indicating any real difference between Council areas. Section C provides information about the results of some comparisons of SHS results with the Census figures for each local authority area, which suggest that the survey's figures should provide reasonable indications of the positions for most Council areas, but they are not precise: the SHS's results may well differ by more than a couple of percentage points from the true values for Council areas. Paragraph 10.7 provides some further guidance on comparing different values from the survey. Please remember that, with so many estimates for each of 32 local authority areas, there may well be occasions on which sampling variability has produced the kinds of results that may arise, purely by chance, in fewer than one sample on twenty (see paragraph 10.9). For ease of reading, the commentary generally gives the survey's estimates without continually reminding you that they may be subject to errors of several percentage points. Similar considerations apply when comparing this edition's figures for one of the local authority areas for 2003/2004 with a previous edition's figures for the same area for an earlier period (1999/2000 and/or 2001/2002). Users of the figures must bear in mind that, the smaller the sample sizes, the greater the possibility that apparent changes are due to sampling variability - for example, it might be that there has been no change in the underlying position in a particular Council area but, purely by chance, the samples in that area produced estimates that were too low in 1999/2000 and too high in 2003/2004, giving an impression of an increase.
2.7 Several improvements have been made for this edition of the bulletin. The main changes are the inclusion of four new tables which provide figures for:
- drivers who make particular types of journey - the percentages who always use a car;
- drivers who always use a car for particular types of journey - whether they could use another means of transport;
- frequency of use of local bus services, and of train services;
- users' views on aspects of local bus services.
In addition:
- some tables include figures for the areas covered by the new Regional Transport Partnerships (instead of the figures for the ad-hoc groupings of local authorities which were used in the previous edition);
- minor improvements have been made to some of the other tables;
- a new section (C) provides some information about comparisons between the SHS and the Census results for local authority areas.
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