Overestimation of chronic disability among elderly persons

Although there is no generally accepted definition for the term short-term disability, chronic disability has been defined as disability lasting or expected to last at least 90 days according to a protocol that was established by the National Long-Term Care Survey. We evaluated the validity of the established protocol and determined the accuracy of prevalence estimates of chronic disability among elderly persons in the United States.

Chronic disability was ascertained during a comprehensive assessment using the established protocol. Participants were subsequently classified as having chronic disability (the gold standard) based on the presence of disability during consecutive monthly interviews immediately before or after the comprehensive assessment.

Of the 552 participants, 120 (21.7%) met criteria for chronic disability according to the established protocol. Of these, 30 (25.0%) and 39 (32.5%) did not meet criteria according to the gold standard under assumptions that were favorable and unfavorable (ie, stringent) to the established protocol, respectively. Conversely, of the 95 participants (17.2%) who met the gold standard criteria for chronic disability according to the favorable strategy and the 89 (16.1%) who met the criteria according to the stringent strategy, 5 (5.3%) and 8 (9.0%), respectively, did not meet criteria for chronic disability according to the established protocol. Relative to the established estimate of 7.0 million, our projections yielded about 2.0 million fewer chronically disabled elderly Americans in 1999.

Our results threaten the validity of the currently established protocol for ascertaining chronic disability and suggest that the burden of chronic disability among elderly Americans has been substantially overestimated.