Use of the mental function index in older adults. Reliability, validity, and measurement of change over time

The Mental Function Index is a weighted combination of scores on three brief tests. The Index was developed to aid in the discrimination of elderly persons with early cases of senile dementia from nondemented elderly individuals. In a previous report (Am J Epidemiol 1981;114:515-27), the authors described preliminary results with the Index in 195 elderly persons in a southern California retirement community. The present study seeks to assess whether similar results can be achieved in samples other than that from which the discriminant function defining the Index was derived. Seven separate studies were done on a total of 210 persons, comprising subjects recruited from a teaching hospital which serves a predominantly lower to lower-middle class population, referrals from the same physicians as in the earlier study, and (for the reliability sample) persons from the upper-middle class community which was the major referral source. It was found that scores on the brief measures correlate 0.86 with those on the three Halstead-Reitan subtests most sensitive to brain damage and to aging. The Index provides a graded measure of disease severity comparable to global neurologic assessment (r = -0.84) and level of social function (r = 0.76). Entry Index is a crude predictor of cognitive status in older adults after several years. Changes in the Index over time parallel those in independent measures of change. The results suggest that the Index will be useful for assessment of disease severity and of longitudinal change, as well as for diagnostic screening, in population studies of senile dementia.