The potential biases in studying the relationship between asthma and microbial infection

To assess bias in parent reports of asthma status of children and detection bias of medical records-based asthma ascertainment and to examine effects of such bias on the association between asthma status and infections.

A prospective cohort study was conducted to compare the correlations between the frequency of acute illnesses and that of medical evaluations between children with or without asthma according to parental report and medical record review by following a group of children who were enrolled in the Mayo Clinic Sick Child Care Program in Rochester, Minnesota. Parents completed a self-administered questionnaire to determine asthma status of their child. Also, comprehensive medical record reviews were conducted to determine asthma status of each subject by applying predetermined criteria for asthma.

A convenience sample of 115 parents and their children participated in this study. The mean age of the parents who participated in the study was 32.8 years (standard deviation: 5.4 years); 93% were female (mothers); and 90% were white. Of the 115 children who participated in this study, 84% were reported to be white and 49% were female. The mean age of the children was 2 years (standard deviation: 1.0 year). Parents whose children had asthma by report appeared to be less likely to seek medical evaluations (Spearman's rho: 0.42,p = 0.11) when their children had acute illnesses, compared to those of non-asthmatic children (rho: 0.64,p < 0.001). Concerns that asthmatic patients (rho: 0.62,p < 0.001) are more likely to see health care providers and undergo medical evaluations and laboratory tests when they have acute illnesses than non-asthmatic patients (rho: 0.64,p < 0.001) are not supported by our study.

Parental report bias needs to be considered carefully when studying the relationship between asthma and microbial infection.