Academic Articles Medical Studies

What are the Major Clinical Pathways to Disability

This is the question posed by a 2007 NBER working paper by Mary Beth Landrum, Kate A. Stewart, David M. Cutler. The authors use data from the National Long Term Care Survey (NLTCS) between 1994 and 1999. The data is panel in nature and has the benefit of combining Medicare administrative data with survey responses. The research examines individuals over 65 without disabilities in 1994 and see which patients became disabled and how this occurred.

Disability is defined by either:

  • 6 specific ADL tasks (eating, getting in and out of bed, getting around inside, dressing, bathing, toileting)
  • 8 specific IADL tasks (light housework, laundry, preparing meals, shopping for groceries, getting around outside, managing money, taking medications, using the telephone)
  • 9 functional limitations (difficulty climbing a flight of stairs, walking across a room, bending to put on socks, lifting a 10-lb object, reaching above the head, using fingers to grasp and handle small objects, seeing well enough to read newsprint, speaking, and hearing)


“Sixty-six percent of non-disabled respondents in 1994 survived and remained non-disabled to 1999, while 15.1% became disabled over the 5 year period and 18.9% died between survey waves. Six conditions made up about half of new disabilities (48%). These conditions were:

  • arthritis,
  • infectious disease,
  • dementia,
  • heart failure,
  • diabetes, and
  • stroke.

Only 17% of elderly respondents did not have one of these conditions and a majority (54%) had two or more. Of disabled respondents, 96% of newly disabled have at least one of these characteristics. Most disabled respondents had multiple conditions; two-thirds of newly disabled respondents had 3 or more conditions. The authors examine in more depth the interaction effects of having two or more conditions. For instance:

“…the interaction between diabetes and arthritis was positive, suggesting that these two conditions have synergistic effects such that having both conditions was more disabling than would be expected by the effects of each individual condition. In contrast, two interactions with dementia were negative (stroke*dementia and heart failure*dementia), suggesting that in the presence of a highly disabling condition like dementia, other conditions have effects that are dampened relative to what would be expected when the disease occurs in isolation.”

Hopefully, this data can be used to aid health service providers on how to better prevent and treat disabilities which occur in old age.