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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 figures relate to the two-year period 2005 and 2006 combined (and, in some cases, to the previous two-year periods 1999/2000, 2001/2002 and 2003/2004) because the SHS, which started in 1999, was designed to provide figures for most local authority areas only for such two-year periods.
2.2 Several improvements have been made for this edition of the bulletin. The main changes are the inclusion of four new tables which provide figures on:
- people's frequency of driving in congested traffic, and how concerned adults are by the increase in the amount of traffic on Scotland's roads - Table 5;
- the possession and use of concessionary fare passes by adults aged 60 and over - Table 14;
- adults' knowledge and use of Traveline Scotland and Transport Direct, and use of motorbikes, mopeds or scooters - Table 15;
- other purposes of drivers' journeys to work - Table 22.
A few of the tables from the previous edition have been dropped in order to make room for the new tables. In addition:
- several tables have been expanded to give figures for the Regional Transport Partnership ( RTP - see section A.7 in the "Notes and Definitions") areas, so there are now figures for RTPs on every one of the topics covered by this bulletin;
- compared with the previous edition, the RTP figures use the more precise definitions which are now incorporated within the SHS database;
- some tables have been reordered, and many have been renumbered;
- the former Tables 11 and 12 are now based on households (rather than the estimated population), for consistency with the former Table 10.
2.3 Statistics are provided for each Council area, each RTP area and 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);
- 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.
2.4 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 ( 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. As it is sometimes not possible to arrange an interview with the randomly-chosen adult, those results are based on smaller sample numbers than the "household-level" analyses. All the results are weighted to take account of differences in selection probabilities. The statistics given here were extracted in October 2007, so will not take account of subsequent revisions to the SHS database.
2.5 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 23 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, so which particular households were selected for inclusion in the sample could make a significant difference to the results: 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 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 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.
2.6 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).
2.7 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, sampling variability may well produce the kinds of results that 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 with those for an earlier period in a previous edition. Users of the figures must bear this in mind: 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 (say) 1999/2000, about right in the next two periods, and too high in 2005/2006, giving an impression of an upward trend.
Chart A: Households with cars available for private use 2005 and 2006
2.8 "Transport across Scotland" is one of a series of Transport Statistics publications, most of which focus on particular aspects of transport and cover them in depth. The individual publications that comprise the series are described in the section on "Transport Statistics publications" towards the end of this edition. A comprehensive statistical picture of transport activity is given by the compendium "Scottish Transport Statistics" volume, the "Main Transport Trends" bulletin and the "Key Transport Statistics" card. These provide figures on a wide range of topics, including: vehicles licensed, traffic volumes and road accidents; the numbers of passengers on bus, rail, air and ferry services; travel to work, travel to school, household car availability and other key findings from the SHS and the National Travel Survey; and the tonnages carried by road, rail and waterborne freight. "Transport across Scotland", "Household Transport" and " SHS Travel Diary results" provide more detailed analyses of the SHS's results on Transport topics.
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