Disability Trajectories at the End of Life: A "Countdown" Model.
OBJECTIVE
Studies of late-life disablement typically address the role of advancing age as a factor in developing disability, and in some cases have pointed out the importance of time to death (TTD) in understanding changes in functioning. However, few studies have addressed both factors simultaneously, and none have dealt satisfactorily with the problem of missing data on TTD in panel studies.


METHODS
We fit latent-class trajectory models of disablement using data from the Health and Retirement Study. Among survivors (~20% of the sample), TTD is unknown, producing a missing-data problem. We use an auxiliary regression equation to impute TTD and employ multiple imputation techniques to obtain final parameter estimates and standard errors.


RESULTS
Our best-fitting model has 3 latent classes. In all 3 classes, the probability of having a disability increases with nearness to death; however, in only 2 of the 3 classes is age associated with disability. We find gender, race, and educational differences in class-membership probabilities.


CONCLUSIONS
The model reveals a complex pattern of age- and time-dependent heterogeneity in late-life disablement. The techniques developed here could be applied to other phenomena known to depend on TTD, such as cognitive change, weight loss, and health care spending.
Aging Studies Institute, Syracuse University, New York. dawolf@maxwell.syr.edu.
Douglas A
DA
Wolf
Institute for Social Research, University of Michigan, Ann Arbor.
Vicki A
VA
Freedman
Center for Policy Research, Syracuse University, New York.
Jan I
JI
Ondrich
Department of Public Health Sciences, University of Rochester School of Medicine and Dentistry, New York.
Christopher L
CL
Seplaki
The Urban Institute, Washington, District of Columbia.
Brenda C
BC
Spillman
D000368:Aged; D000369:Aged, 80 and over; D000375:Aging; D003643:Death; D006233:Persons with Disabilities / Q000145:classification / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D008297:Male; D013997:Time Factors; D014481:United States / Q000453:epidemiology
Disability; Latent classes; Time to death; Trajectories