Estimates of minimal clinically important differences in health measures may be affected by the anchor used. We examined if domain-specific transition questions had higher construct validity than global health transition questions as anchors for measures in a given domain.
In a prospective study of 249 patients with rheumatoid arthritis, we examined changes in pain, physical function, joint swelling, stiffness, fatigue, and depression with treatment. We related these changes to a domain-specific transition question, global arthritis transition question, and the Short Form-36 (SF-36) health transition item.
Changes in all six clinical measures were more highly correlated with the domain-specific transition questions than with the global arthritis question and SF-36 transition question. Discrimination between patients who improved or not was also better using domain-specific questions. Estimates of minimal clinically important improvement (MCII) differed with the anchor when these were based on mean changes. MCII estimates from receiver operating characteristic curve analysis were not influenced by the choice of anchor when anchors had high agreement.
Domain-specific transition questions had higher construct validity as anchors for determining clinically important differences in health measures focused on a single domain than either global disease or general health transition questions.