First, a crude model with the eight specific dimensions
of illness perceptions (model 1) was analysed. In the second model (model 2), illness perceptions were corrected for the confounders of age and gender. In the
third model (model 3), illness perceptions were adjusted
for dyspnoea, airflow reduction (FEV1%predicted) and
comorbidities. In the regression models, the standardised
βs were used to compare the strength of the various independent variables. The adjusted explained variance
(adjusted R2) per model was then analysed. Because only 3% of the data was missing, a complete case analysis was performed. All analyses were performed with the Statistical Package for the Social Sciences (SPSS 20.0 for Windows).