Outcome of interest
Our outcome of interest was the onset of asthma during the follow-up
period. In the baseline and 6-year follow-up surveys, this was
determined with the following question: “Has the child ever had
physician-diagnosed asthma?” If the answer was yes, the age at
diagnosis was requested. The following questions were asked in the
20-year follow-up: “Have you ever had physician-diagnosed asthma? If
yes, at what age was it diagnosed?”