The US NHANES is one of the very few community-based representative surveys in the world with a variety of self report and body measures. Recent NHANES datasets have provided opportunity to compare differences of physical function within the same population over the time period of 5to 10 years. This study aims to evaluate the change of physical function, measured by both self-report and performance tests, during the last decade. Respondents aged60 and over in the NHANES III and 1999-2000 were included in the analysis. There was no difference on age and sex between two datasets. 12 daily tasks, which were all measured in the same manner, were classified into three domains, mobility, IADL, and ADL. Timed walk test was employed to measure mobility function. With regard to proportion of functional difficulties of respondents (no or with difficulty), there was no difference in performing nearly all tasks between two surveys. However, the proportion for older people unable to perform the tasks (being able or unable) decreased and statistical significance were found in five of these tasks (walking 1/4 mile and up 10 steps, stooping, lifting 10 pounds, and doing chores). Results in comparing both datasets on timed walk test showed an obvious improvement in walking ability (0.79 vs. 0.93m/sec). The prevalence of physical difficulty did not change but people reported with difficulty were less disabled, which reflects on better mobility ability in the NHANES 1999-2000. Further analyses are needed to explore the possible causes of differences in physical function.
