[Comorbidity from the patient perspective - does it work? Validity of a questionnaire on self-estimation of comorbidity (SCQ-D)].

To minimize the medical effort for the measurement of comorbidity, which is a relevant factor for various outcome measures, the Self-Administered Comorbidity Questionnaire (SCQ) for patient self-evaluation has been developed. After successfully testing the psychometric characteristics and content of the original English version a validation of the German translation (SCQ-D) has so far been lacking. A total of 218 patients with gonarthrosis and coxarthrosis (average age 71.5 years) were included in the survey. A questionnaire for doctors as well as patients was used to collect data at five different measurement times (postoperative, beginning and end of rehabilitation as well as 4 months and 1 year postoperatively). To evaluate the matching of comorbidities according to the SCQ-D and the Charlson Comorbidity Index (CCI), aggregate indices for "problems" and "treatment" as well as correlation and kappa coefficients were calculated. The assessment of predictive validity in terms of treatment outcome was operationalized using the WOMAC and the postoperative 1 year hospitalization by applying multilevel models. The patient self-assessment using the SCQ-D correlated well with the physician assessment using CCI in terms of aggregate indices of 13 given disease groups with r = 0.49 (problems) and r = 0.48 (treatment). However, the results showed significant differences for certain diseases in the conclusions. The comorbidity measured by the SCQ-D proved to be a valid predictor of the hospitalization and the treatment outcome. Concerning the need for resource efficient data collection especially in large sample studies, the SCQ-D is a useful patient self-administered instrument to assess the type and extent of comorbidities.