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Survey design

In the course of time there have been a number of changes in the NTS. These concern the sample framework, the method of recruitment, the way of reminding in the case of non-response, the layout of the questionnaire/journey diary, the wording of questions and possible answers, follow/-up surveys, and the sample size.

The NTS underwent such large changes in 1985, 1994, and 1999. That is why the series do not match anymore. There has not been a social change in the Netherlands (a trend break) but a change in the observation instrument of the exposure development. The term 'trend break' is often used for both, whereas for the second one a 'method break' would be a better term.

The 1978-1884 period is no longer comparable with the following period.

In 1994 the sample size was increased and children were included.

The idea behind the 1999 change is that after the change the NTS design describes the reality better than previously. The 1985-1998 data has been corrected for the 1999 trend break.

In the following paragraphs the 1985-1998 and 1999-2004 periods will be dealt with separately, if necessary.

The NTS does not contain journeys for:

CBS, however, publishes estimates of domestic holiday traffic and an estimate of the journeys of children (0-11 years old) by region and by mode of transport for the 1985-1993 period.