Information on the health of sampled children was collected in 1991 from both mother�s reports and medical records. The information spanned the child�s lifetime.

Mothers were asked to check whether they had ever been told their child had each of a list of 14 chronic health conditions, including asthma.

Medical records were obtained for all of the child�s visits through 1991. Medical providers had the option of filling the information for each visit into a survey form sent by the National Center for Health Statistics, or attaching a copy of the medical records for the sampled child. A doctor�s diagnosis of asthma was based on mention of asthma in either a checklist of possible conditions, or a listing of asthma by name or ICD-9 code (493.0) as a diagnoses for any visit.