What are we measuring? An examination of self-reported functional status measures.

Functional status questionnaires are being used in various types of studies. To determine factors related to self-reported functional ability for rheumatoid arthritis patients, we examined the relationship between a functional and mental health questionnaire and objective disease-specific measures. Using 3-5 predictor variables, we explained 43-57% of the variance in patients' self-reported functioning. Mental and physical health perceptions were significant predictors for each self-reported functional measure. The relationships among mental health and self-reported functioning should be considered when interpreting studies that use functional status questionnaires.