13: Mixed Mode Surveys

Concerns about compatibility of data derived from different survey instruments are far from trivial. Such issues assume considerable importance when attempting to answer many questions that typically confront transport planners. Ideally, attempts to draw comparisons between survey findings pertaining to one place and those of another, or between two different time-periods, would only be made where there is consistency of approach and methods. In reality, however, information is frequently drawn from many different sources, and then compared and sometimes combined. These sources may have significant differences, including differences in methodology. Where methodological differences in data collection exist, it is important to try to account for the differences in observed outcomes that arise directly from the survey methodology – or at the very least, to acknowledge that such methodological differences exist.