To examine the agreement between and compare the sensitivity to change of the Arthritis Impact Measurement Scale (AIMS2) and AIMS2 Short Form (AIMS2-SF) in a large sample of rheumatoid arthritis (RA) patients examined within the framework of a longitudinal observational study.
Data were collected from patients in a community based RA register by a postal survey in April 1994 (1,030 respondents) and again in 1996 (1,153 respondents), comprising AIMS2, Modified Health Assessment Questionnaire (MHAQ), Medical Outcome Survey SF-36, and other commonly used health status measures. The degree of agreement was examined by plotting differences between AIMS2 and AIMS2-SF against the mean of the 2 scores for the 5 main components. The upper and lower limits of agreement (mean diff. +/- 1.96 SD) were calculated and plotted. The intraclass correlation coefficients were computed by repeated measurement ANOVA. Validity was assessed on the basis of external indicators of health status, and responsiveness on the basis of standardized response means.
The AIMS2 and AIMS2-SF showed substantial to near-perfect agreement. Best agreement was seen for the physical and affect components. Better agreement for the symptom component was obtained when replacing item 42 with item 38. Internal consistency was high in all components. The 2 forms correlated similarly with scores from other instruments within the same domains, showing similar construct validity. There was no difference in responsiveness between the 2 forms when using changes in patient assessed global disease activity as external indicator of change in health status, and responsiveness for the physical and symptom dimension was similar to other instruments (SF-36, MHAQ).
The AIMS2-SF is amenable for use in large surveys with a modification of one item in the symptom scale.