Context: Measurement of change in patients' health status is central to both clinical trials and clinical practice. Trials commonly use serial measurements by the patients at 2 points in time while clinicians use the patient's retrospective assessment of change made at 1 point in time. How well these measures correlate is not known.
Objective: To compare the 2 methods in measurement of changes in pain and disability.
Design: Longitudinal survey of patients starting new therapy for chronic arthritis in 1994 and 1995. Surveys were completed at baseline (before intervention) and at 6 weeks and 4 months.
Setting: Community health education program and university medical and orthopedic services.
Subjects: A total of 202 patients undertaking self-management education (n = 140), therapy with prednisone or methotrexate (n = 34), or arthroplasty of the knee or hip (n = 28).
Main outcome measures: Concordance between serial (visual analog scale for pain and Health Assessment Questionnaire for disability) and retrospective (7-point Likert scale) measures, sensitivities of these measures, and their correlation with patients' satisfaction with the change (7-point Likert scale).
Results: When change was small (education group), serial measures correlated poorly with retrospective assessments (eg, r=0.13-0.21 at 6 weeks). With greater change, correlations improved (eg, r = 0.45-0.71 at 6 weeks). Average agreement between all pairs of assessments was 29%. Significant lack of concordance was confirmed in all 12 comparisons by McNemar tests (P = .02 to <.001) and by t tests (P = .03 to <.001). Retrospective measures were more sensitive to change than serial measures and correlated more strongly with patients' satisfaction with change.
Conclusion: The 2 methods for measuring health status change did not give concordant results. Including patient retrospective assessments in clinical trials might increase the comprehensiveness of information gained and its accord with clinical practice.