Exploring disability rating scale responsiveness II: do more response options help?

The Barthel Index (BI) may underestimate disability change because its items have few response options. We examined whether a similar scale with more response options (Functional Independence Measure, FIM) was more responsive (n = 1,396). The FIM had greater potential for responsiveness and identified more people who changed. However, its actual responsiveness, measured by effect sizes, equaled that of the BI. This counterintuitive finding suggests that effect sizes may be limited indicators of responsiveness.