To examine the psychometric properties and construct validity of a self-administered Rheumatoid Arthritis Disease Activity Index (RADAI).
Five items of the Rapid Assessment of Disease Activity in Rheumatology (RADAR) questionnaire were aggregated into the RADAI and assessed for their factor loading, internal consistency, and construct validity.
In 55 patients with RA, the RADAI had a high internal consistency (Cronbach's alpha = 0.91) and correlated with physician's assessment of disease activity (r = 0.54, P < 0.01), the swollen joint count (r = 0.54, P < 0.01), and the C-reactive protein value (r = 0.43, P < 0.01).
The RADAI is a highly reliable and valid self-administered measure of disease activity for clinical, health services, and epidemiologic research. Its sensitivity to change in longitudinal studies needs further study.