Disability in rheumatoid arthritis: comparison of prognostic factors across three populations.

We previously identified variables that predict functional disability in rheumatoid arthritis (RA). Because of potential instabilities in the statistical model, we sought to determine whether these predictors were consistent across populations: 2,448 consecutive patients with (RA) were followed prospectively at ARAMIS centers in Phoenix, AZ, Wichita, KS, and Saskatoon, SK. Average followup was 1.7 years in Phoenix, 3.4 years in Wichita, and 12 years in Saskatoon. Twenty-four potentially predictive variables were analyzed by stepwise linear regression. Common predictors were age, sex, and duration of illness, suggesting that these variables are important predictors of disease regardless of the population being studied. In addition, the initial level of disability and radiographic variables are good predictors of disability. Elevated erythrocyte sedimentation rate and latex titers also were associated with future functional disability but do not have a linear relationship and predict less well.