Guidelines for Samplers: Measuring a Change in Behaviour from Before and After Surveys

Before and after studies are not frequently used to evaluate transportation policies and investments. This paper discussing the use of this type of study to evaluate behavioral changes in response to transport policies and investments and demonstrates that there are almost always considerable economies to be obtained by using a panel to undertake evaluation rather than successive independent cross-sectional surveys. The paper also addresses the issue of sample size requirements for measuring changes of a relatively small magnitude in travel behavior; i.e., to state, with 95% confidence, that if there is a ∂ percent change in behavior for the sample, there is a ∂ percent ± e percent change in the behavior of the population, where e is the sampling error. A method is presented for calculating such sample size requirements from first principles and the applicability both hypothetically and then empirically using data from the Puget Sound Transportation Panel is demonstrated. The formulation enables designers of before and after surveys to investigate the trade-offs between the statistical accuracy of their predictions and the sample size requirements systematically, without the need to specify ∂ a priori. The authors indicate that this latter point is crucial because we have limited information on ∂, yet it drives the sample size requirements. This method is also statistically sound for assessing and interpreting the results of previous behavioral change programs.

  • Availability:
  • Authors:
    • Stopher, Peter R
    • Greaves, Stephen P
  • Publication Date: 2007-1


  • English

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  • Accession Number: 01044722
  • Record Type: Publication
  • Files: TRIS, ATRI
  • Created Date: Mar 29 2007 8:04PM