National surveys of older Americans routinely have included functional limitation items using either a leading approach ("how much difficulty do you have...") or a neutral approach ("do you have any difficulty..."). This article evaluates the performance of scales based on these two approaches.
Methods: Using responses from 595 randomly selected participants to the 1994 Health and Retirement Study, the authors compared prevalences and evaluated scales based on each approach with respect to the extent of missing data, face validity, reliability, predictive validity, convergent validity, and robustness of odds ratios in predictive models.
Results: The authors found that leading questions provided higher estimates of functional limitations than neutral questions, but both approaches yielded scales with similar validity and reliability. However, for both approaches, scales incorporating degree of difficulty had better validity and reliability than those based on counts of tasks. All four approaches yielded substantially similar coefficients in a model predicting disability onset.
Discussion: The authors conclude that, because they minimize survey time without compromising validity and reliability, items that explicitly capture degree of difficulty by asking "How much difficulty do you have..." may be the optimal approach for survey designers.