Objective: To quantify the misclassification bias of self-reported somatic diseases and its impact on the estimation of comorbidity with mental disorders.
Study design and setting: Data were drawn from the German National Health Interview and Examination Survey (N=7,124), which assessed both self-reported and physician-diagnosed somatic diseases. Eight chronic diseases were examined: coronary heart disease, heart failure, asthma, chronic bronchitis, diabetes, cancer, arthrosis, and arthritis. Mental disorders were assessed by means of the Munich-Composite International Interview.
Results: The agreement of case ascertainment by patient self-report and physician diagnosis was high (kappa: 0.74-0.92), except for arthritis (0.53). False-positive and false-negative disease statuses were partly associated with age, sex, socioeconomic status, somatic comorbidities, marital status, and mood and anxiety disorders. In most conditions, the odds ratios (ORs) of comorbid mental disorders based on self-reported diseases were slightly overestimated with regard to mood disorders (relative OR: 0.91-1.38), whereas there proved to be no such trend regarding anxiety disorders (0.82-1.05). Substance disorders were partly biased without showing an interpretable trend across diseases (0.49-2.58).
Conclusions: Evaluation of mental-physical comorbidity based on self-reported and physician-diagnosed physical conditions yielded similar results, with modestly inflated ORs for mood disorders for several self-reported physical conditions.