Comparison of predictive value of activity limitation staging systems based on dichotomous versus trichotomous responses in the Medicare Current Beneficiary Survey

Jibby E. Kurichi, M.P.H., Joel E. Streim, M.D., Hillary R. Bogner, M.D., M.S.C.E., Dawei Xie, Ph.D., Pui L. Kwong, M.P.H., Sean Hennessy, Pharm.D., Ph.D.

Disability and Health Journal, Volume 9, Issue 1, p. 64–73



Traditional ways of measuring disability include summary indices, binary expressions, or counts of limitations. However, counts of activity of daily living (ADL) or instrumental activity of daily living (IADL) limitations do not specify which activities are limited. Activity limitation staging systems within the ADL and IADL domains depict both the severity and types of limitations experienced and specify clinically meaningful patterns of increasing difficulty with self-care.


To compare the predictive value and utility of ADL and IADL stages based on dichotomous versus trichotomous responses to ADL and IADL questions based on “difficulty” and “receive help” responses.


Data were analyzed from the 2005, 2006, and 2007 Medicare Current Beneficiary Survey (MCBS) entry panels on 11,706 beneficiaries. This was a prospective cohort study that examined time to inpatient admission, all-cause mortality, skilled nursing facility (SNF) admission, and long-term care (LTC) facility admission based on dichotomous versus trichotomous stages.


For both ADLs and IADLs, Akaike information criteria for most outcomes were lower (indicating better-performing models) for the trichotomous staging systems than the dichotomous staging systems. The hazard ratios (HRs) and 95% confidence intervals (CIs) of the dichotomous ADL staging system increased as disability increased, whereas the HRs of the other staging systems fluctuated.


Both staging systems have strong associations with each outcome. The dichotomous staging system is more clinically relevant while the trichotomous staging system may provide utility for clinicians, health care organizations, and policy makers seeking to predict death or admission to a hospital, SNF, or LTC facility.