Because follow-up surveys were obtained from all 28
children (+1 dropout), an additional recruitment period
was waived. A possible explanation for observing no dropouts
is that the trainer maintained close, personal contact
with participating families, including repeated reminders of
appointments. Furthermore, a reward contract included regular
completion of the questionnaires and the diary. Thus,
the possibility of a biased sample with highly motivated
participants exists. However, to prove these interpretations,
data are lacking.