Risk Factors for Disability Subtypes in Older Persons

OBJECTIVES: To identify risk factors for five different subtypes of disability. DESIGN: Prospective cohort study. SETTING: Greater New Haven, Connecticut. PARTICIPANTS: Seven hundred fifty-four community-living residents aged 70 and older and initially nondisabled in four essential activities of daily living (bathing, dressing, walking, and transferring). MEASUREMENTS: Candidate risk factors were measured every 18 months for 90 months during comprehensive home-based assessments. Disability was assessed during monthly telephone interviews for up to 108 months. In participants who were nondisabled at the start of an 18-month interval, incident episodes of five different disability subtypes were determined during the subsequent 18 months: transient, short-term, long-term, recurrent, and unstable. RESULTS: The cumulative incidence rates per 100 person-intervals were 9.8 (95% confidence interval (CI)=8.9-10.6) for transient disability, 3.8 (95% CI=3.3-4.3) for short-term disability, 7.1 (95% CI=6.4-7.8) for long-term disability, 4.7 (95% CI=4.1-5.3) for recurrent disability, and 4.4 (95% CI=3.9-5.0) for unstable disability. In a multivariate analysis, the Short Physical Performance Battery (SPPB) was associated with each of the five disability subtypes, with adjusted hazard ratios ranging from 1.10 for transient disability to 1.35 for long-term disability. The only other factors associated with short-term, long-term, and recurrent disability were stroke, visual impairment, and poor grip strength, respectively. Transient disability and unstable disability shared the same set of risk factors-depressive symptoms, stroke, and poor grip strength-in addition to the SPPB. CONCLUSION: These results provide mixed evidence to support the distinct nature of the five disability subtypes.