2. Introduction to the Scottish Household Survey and the Travel Diary
2.1 These statistics were obtained from interviews with a randomly-chosen adult in a household. The respondent was asked about their travel on the previous day. Each adult in the household had an equal chance of selection. .
2.2 The results have been weighted to take into account differences in selection probabilities. Un-weighted sample numbers are given in italics.
2.3 Results are subject to sampling variability and care should be taken when interpreting year on year changes - confidence limits for the estimates are presented in Table 32 and should be considered when looking at changes. A detailed background of the SHS methodology is given in Appendix A.
2.4 Although the total number of interviews was evenly spread across the week, this is not the case at the local authority level [ Table 31] Therefore, any analysis by day of week should be treated with caution .
Methodological Changes - 2007 data onwards
2.5 A number of changes were made to the Travel Diary from 2007 onwards, these changes are as follows:
- Journeys less than 1/4 mile or shorter than 5 minutes on foot are now reported - reduces under reporting of short (likely to be) walking journeys;
- Introduction of improved weighting system accounting for non-response bias.
- 3/4 of the main SHS are now asked the Travel Diary element - previously all the households had been asked.
- Improvements to wording of questions - reduces under reporting of journeys.
- Improvements to quality of data - e.g. duration of journey asked instead of calculated.
2.6 The above changes mean that some time series tables may not be entirely comparable. The main impact is a higher proportion of short journeys, which are mostly walking journeys. Therefore mode and distance/duration tables are most effected.
2.7 Further detail of these changes are discussed in the Appendix and analysis of the impact of these will be available on the website soon. www.scotland.gov.uk/Topics/Statistics/Browse/Transport-Travel/PubSHSTravDiary