Unadjusted Prevalence Rates: Why they Still Matter for Older Adults' Disability Rates

We thank Martin and colleagues for their thoughtful and important comments. We very much appreciate their supplementary age-standardized analysis of the public use American Community Survey (ACS) data. Their findings give support to our suggestion (1) that the rise in prevalence of activities of daily living (ADL) disabilities between 2000 and 2005 among those aged 65 and older was largely driven by the disproportion ate growth in the oldest age category. Their findings also have important ramifications in the pro jection of the burden of disabilities in the American population aged 65 and older. Projections suggest that the percentage of senior citizens who are older than age 85 will increase from 12.2% in the year 2000 to 24.1% in the year 2050 (2). We deliberately chose to report the crude (unadjusted) trend in prevalence for those aged 65 and older rather than age-adjusted figures for two reasons. Most importantly, the govern ment is currently mandated to provide assistance in many programs (eg, Medicare) to those aged 65 and older. Therefore, it is the unadjusted prevalence rate of disability that is a measure of the burden of care and is of immediate salience to policy makers. Secondly, our report is in keeping with a National Institute of Aging funded technical working group that chose to compare unadjusted estimates of disability across five national data sets (3). This group justified its decision to use crude rates because “conclusions about standardized rates are sensitive to the choice of age distribution” and “stratifica tion by age, gender and other subgroups of interest leads to an unmanageable number of comparisons.” (3, p. 421). Martin and colleagues also raised the concern that the change in interview mode between 2000 and 2005 made our estimates of trends in disability unreliable. We did a sensitivity analysis of the relative change and find it unlikely that the change in mode would substantially alter our results. Unfortunately, we did not have access to information on interview mode for the population aged 65 and older. How