title: Functional ability indices: measurement problems in assessing their validity.
abstract: This study examines measurement problems which must be considered in assessing the validity of alternative measures of functional ability. Threats to meaningful evaluation of validity include problems of: (1) assessing the impact of aids, adaptations and helpers; (2) controlling for situational variation and motivational factors; (3) controlling for the professional perspective of the rater; and (4) controlling for the role expectations of the patient in the performance of certain functions. These problems were investigated using validity comparisons from the St. Thomas' Hospital elderly study in which questionnaire-based assessments of functional status were compared with assessments of physicians and visiting geriatric nurses. Clinician and questionnaire-based measurements were compared for 92 elderly (age 75 years and older) primary-care patients in terms of performance of 13 mobility and self-help functions. Trichotomous measures of performance controlled more adequately for the compensating effect of aids, adaptations, and helpers, and rater/questionnaire agreement was highest for more basic mobility and self-help functions. Test-retest reliability comparisons indicated that motivational factors and situational variation were minimized by reassessing the subjects in their own homes using members of their primary-care team. Levels of concordance between questionnaire ratings and clinical ratings show systematic variation indicating differences in the clinical perspectives of physicians and visiting nurses. Finally, variations in the reported and clinically-evaluated performance of male and female subjects appear to reflect the culturally determined role expectations of men and women as they relate to self-care.
mesh_terms: D000203:Activities of Daily Living; D000368:Aged; D005260:Female; D006262:Health; D006304:Health Status; D006801:Humans; D008297:Male; D009043:Motor Activity; D012046:Rehabilitation