Reproducibility of an extensive self-report questionnaire used in secondary coronary prevention

AIMS: Self-reported information from questionnaires is frequently used in clinical epidemiological studies, but few provide information on the reproducibility of instruments applied in secondary coronary prevention studies. This study aims to assess the test-retest reproducibility of the questionnaire applied in the cross-sectional NORwegian CORonary (NOR-COR) Prevention Study. METHODS: In the NOR-COR study 1127 coronary heart disease (CHD) patients completed a self-report questionnaire consisting of 249 questions, of which there are both validated instruments and de novo questions. Test-retest reliability of the instrument was estimated after four weeks in 99 consecutive coronary patients. Intraclass Correlation Coefficient (ICC) and Kappa (κ) were calculated. RESULTS: The mean interval between test and retest was 33 (±6.4) days. Reproducibility values for questions in the first part of the questionnaire did not differ from those in the latter. A good to very good reproducibility was found for lifestyle factors (smoking: κ = 1.0; exercise: ICC = 0.90), medical factors (drug adherence: ICC = 0.74; sleep apnoea: ICC = 0.87), and psychosocial factors (anxiety and depression: ICC = 0.95; quality of life 12-Item Short-Form Health Survey (SF12): ICC = 0.89), as well as for the majority of de-novo-created variables covering the patient's perceptions, motivation, needs, and preferences. CONCLUSIONS: The present questionnaire demonstrates a highly acceptable reproducibility for all key items and instruments. It thus emerges as a valuable tool for evaluating patient factors associated with coronary risk factor control in CHD patients.