Cognitive Performance Test: a new approach to functional assessment in Alzheimer's disease.

A new performance-based assessment instrument for evaluating function in patients with Alzheimer's disease (AD), the Cognitive Performance Test (CPT), is described. This instrument, based on Allen Cognitive Disability Theory, uses six common activities of daily living (ADL) tasks, for which the information-processing requirements can be systematically varied to assess ordinal levels of functional capacity. Seventy-seven patients with mild to moderate Alzheimer's disease (AD) and 15 neurologically normal elderly controls were administered the CPT. Subsets of the AD patients were assessed again at 4 weeks and 1, 2, and 3 years following the initial evaluation. Internal consistency of the CPT estimated by alpha was .84. Intraclass correlation for interrater reliability was .91 and for test-retest reliability at 4 weeks, .89. CPT scores were significantly correlated with Mini-Mental State Examination scores (r = .67) and two measures of caregiver-rated ADL (Instrumental Activities of Daily Living, r = .64; Physical Self-Maintenance Scale, r = .49). Significant declines in CPT scores were seen on 1-, 2-, and 3-year follow-ups. Initial CPT scores predicted risk of institutionalization over a 4-year follow-up period.