Strengths and weaknesses
weakness
The strengths of our study include the objective definition of AST, which takes into account combined transport modes. To our knowledge, this is the only study assessing perceived barriers to AST for schoolchildren across the whole age span from 1A weakness is that we could not control for possible cluster effects on the neighbourhood, school or family level, as the sample sizes per cluster did not permit this (e.g., the most frequented school in our sample accounted for less than 3% of participants). There was also a discrepancy in the phrasing of questions: The questions regarding barriers referred to independent active travel, whereas the transport mode question focused on the active/passive transportation mode, ignoring the aspect of independence.Since our data collection was based on electronic case report forms, we were methodologically unable to survey children younger than 10 years, an age when they were not yet confident reading and using a computer. We also assume lower independence at that age. Therefore, the statements of the parents seemed to be of primary importance. Finally, the generalizability of our results might be limited because of the underrepresentation of participants with a low SES and because majority of participating families lived in an urban environment.