Asthma and health-related quality of life - effect of adjusting for potential confounders

Health-related quality of life (HRQoL) is an increasingly important outcome measure in medical research. We wanted to evaluate how adjustment for potential confounders affected the relationship between HRQoL and asthma. Furthermore, we wanted to evaluate the relationship of environmental tobacco smoke (ETS) with HRQoL.

We carried out a cross-sectional Norwegian community study in 1996/1997 including 2306 randomly selected subjects aged 26 years-81 years. Data on HRQoL were measured by SF-12. The data were analyzed by robust linear regression analyses with the physical component score (PCS) and the mental component score (MCS) as dependent variables. The effect of adjusting for the potential confounders was analyzed by bootstrap confidence intervals for differences between the adjusted and unadjusted models.

The difference in the asthma coefficients between the unadjusted and adjusted models for both PCS and MCS varied from 0.1 to 1.1. The confidence intervals for these differences for PCS were (-0.3, 1.6) and (0.4, 1.8), using the definition 'asthma last 12 months' and 'physician's diagnosis of asthma', respectively. The confidence intervals for the corresponding differences for MCS were (-0.01, 1.3) and (-0.6, 0.4), respectively. Univariately, PCS was lower among subjects reporting ETS at home compared to people not reporting ETS at home, but this difference did not persist in the multivariate analyses. ETS at home was associated with slightly improved MCS.

Adjusting for potential confounders does not change the relationship between asthma and HRQoL overtly.