Five health status instruments were administered in random order to 50 arthritis patients before and after total joint arthroplasty. Relative efficiency and sensitivity in measurement of change in pain, mobility and physical function, social role and social activity, and global health were assessed. The instruments had highly correlated scores, but had differences in certain dimensions. Inter-instrument differentials were larger for social and global outcomes than for pain or mobility. NO single instrument consistently outperformed the others. A method for determining relative efficiency is described.