Objectives: To adapt the self-administered comorbidity questionnaire (SCQ) into the Early Inflammatory Arthritis-SCQ (EIA-SCQ) and assess its clinimetric properties in EIA.
Methods: The EIA-SCQ and indices of disease activity, function, pain, health-related quality of life (HRQoL) and health resource utilization were administered to 320 patients with EIA. Twenty patients completed the EIA-SCQ a second time 1 week later. Construct validity was evaluated by testing the hypotheses that a valid comorbidity index would correlate well with age, weakly with HRQoL and recent resource utilization and poorly with indices of disease activity, function and pain.
Results: The intra-class correlation coefficient between repeat scores was 0.93 (95% CI 0.83-0.97). Kappa values for individual items ranged from 0.64 to 1.0. EIA-SCQ scores correlated moderately with age (Tau B = 0.29, P < 0.001) and weakly with function (HAQ-DI Tau B = 0.09, P = 0.03), pain (McGill Pain Questionnaire Tau B = 0.09, P = 0.05), some measures of HRQoL [the SF-36 mental component score (MCS) Tau B = - 0.08, P < 0.05; World Health Organization Disease Assessment Schedule II score Tau B = 0.09, P = 0.03] and a measure of resource utilization (number of tests in the last 4 months Tau B = 0.10, P = 0.04). The EIA-SCQ did not correlate with other measures of disease activity, another HRQoL measure [SF-36 physical component score (PCS)] or other measures of resource utilization.
Conclusions: The EIA-SCQ is reliable and valid for use in EIA. It has the potential to become a useful measure of comorbidity in outcome studies of EIA when the resources for a full medical chart review are unavailable.