Longitudinal Care Patterns For Disabled Elders: A Bayesian Analysis of Missing Data

The growth in the number of dependent elderly and the concurrent decline in the availability of informal caregivers has led to increasing concern that use of publicly-funded long-term care services will rise, as community-residing elders substitute these formal services for informal care. To investigate the extent of service substitution and identify correlates, longitudinal data from a study of elders and their informal caregivers were analyzed. Over 50% of subjects were missing the outcome of interest, although only 8% had no partial outcome data. This paper compares results from three missing-data methods: complete-case analysis, single regression imputation, and multiple regression imputation. Prior assumptions regarding the distribution of the outcome among nonrespondents were varied in order to examine their effect on the estimates. Regardless of the prior assumptions, 22%–23% of elders were estimated to substitute formal services for informal care. Substitution was associated with greater demands on and lower availability of informal caregivers, occurring primarily in situations where the need for care exceeded the capacity of the informal care network. Imputation provided a straightforward means of estimating the probability of substitution among a subgroup of nonrespondents not represented among respondents. In addition, multiple imputation incorporated uncertainty about nonrespondent parameters.