Study participants were not aware of this study hypothesis, and occupational biography is an unprejudiced variable, so reporting bias is unlikely to occur.
Three observers, aware of the hypothesis being tested, viewed and scored the first group of data collected according to the behavioral categories listed in Table 2.
While symptoms were self-reported, parents were not obviously aware of the hypothesis investigated here at the time of the original survey.
It can be argued, however, that this is unlikely to be an important consideration for an exposure such as recall of age at menarche, unless patients are aware of the hypothesis.
Strengths of the present study were the prospective design, the inclusion of 5 different European countries, the standardized and comprehensive assessments of growth, and that neither participants nor examiners were aware of the hypothesis tested here.
Secondly, the data collectors might have introduced bias during the interview but, since they were not aware of the hypothesis being tested, its effect is thought to be little.
While it is true that parents who might worry about the effect of exposure to traffic pollution might exaggerate their children's health experiences, it should be noted that at the time of the original survey participants were not aware of the hypothesis investigated here.
Some recall bias may have been possible with respect to past medical history and respiratory exposures, but, even if present, these are more likely to have been non-differential between those with adequate and inadequate glucose control (subjects were not aware of the hypothesis under study).
