Risk factors and precipitants of long-term disability in community mobility: a cohort study of older persons

Abstract

Background: Relatively little is known about why older persons develop long-term disability in community mobility.

Objective: To identify the risk factors and precipitants for long-term disability in walking a quarter mile and driving a car.

Design: Prospective cohort study from March 1998 to December 2009.

Setting: Greater New Haven, Connecticut.

Participants: 641 persons, aged 70 years or older, who were active drivers or nondisabled in walking a quarter mile. Persons who were physically frail were oversampled.

Measurements: Candidate risk factors were assessed every 18 months. Disability in community mobility and exposure to potential precipitants, including illnesses or injuries leading to hospitalization or restricted activity, were assessed every month. Disability that lasted 6 or more consecutive months was considered long-term.

Results: 318 (56.0%) and 269 (53.1%) participants developed long-term disability in walking and driving, respectively. Seven risk factors were independently associated with walking disability and 8 were associated with driving disability; the strongest associations for each outcome were found for older age and lower score on the Short Physical Performance Battery. The precipitants had a large effect on long-term disability, with multivariate hazard ratios for each outcome greater than 6.2 for hospitalization and greater than 2.4 for restricted activity. The largest differences in absolute risk were generally observed in participants with a specific risk factor who were subsequently hospitalized.

Limitations: The observed associations may not be causal. The severity of precipitants was not assessed. The effect of the precipitants may have been underestimated because their exposure after the initial onset of disability was not evaluated.

Conclusion: Long-term disability in community mobility is common among older persons. Multiple risk factors, together with subsequent precipitants, greatly increase the likelihood of long-term mobility disability.

Primary funding source: National Institute on Aging, National Institutes of Health.

Figure 1

Absolute risk differences for precipitants and risk factors independently associated with long-term disability in walking a quarter mile. Values for the risk factors are provided according to the absence or presence of the two precipitants. Point estimates are accompanied by nonparametric 95% confidence intervals. The absolute risk difference represents the absolute risk of developing the outcome when the risk factor is present minus the base risk, which is the average probability of developing the outcome when all of the risk factors and precipitants in the final multivariable model are set to their reference level, namely no precipitant, age 70–74 years, male sex, no chronic conditions, MMSE score ≥ 24, functional self-efficacy score > 27, PASE score ≥ 64 for men and ≥ 52 for women, and SPPB score ≥ 10. The base risk for long-term walking disability is 3.7%. For the ordinal risk factors, absolute risk differences are provided only for the levels that had achieved statistical significance at P < .05 in the final model.

Figure 2

Absolute risk differences for precipitants and risk factors independently associated with long-term disability in driving a car. Values for the risk factors are provided according to the absence or presence of the two precipitants. Point estimates are accompanied by nonparametric 95% confidence intervals. The absolute risk difference represents the absolute risk of developing the outcome when the risk factor is present minus the base risk, which is the average probability of developing the outcome when all of the risk factors and precipitants in the final multivariable model are set to their reference level, namely no precipitant, age 70–74 years, male sex, mild or no visual impairment, no significant weight loss, MMSE score ≥ 24, PASE score ≥ 64 for men and ≥ 52 for women, SPPB score ≥ 10, and gross motor coordination time < 8.8 seconds. The base risk for long-term driving disability is 4.1%. For the ordinal risk factors, absolute risk differences are provided only for the levels that had achieved statistical significance at P < .05 in the final model.