Do actions speak louder than words? Self-assessed and performance-based measures of physical and visual function among old people.

Self-assessments and performance-based tests are methods commonly used to assess physical function in health surveys of older people. It has been suggested that the choice of method could affect the results, particularly in certain groups. This study compares results attained using self-assessed and performance-based measures of upper and lower body function and vision. The influence of sex, age, education and cognitive status is explored. This is done by studying the prevalence rates of self-reported and observed limitations in function, the prevalence rates of discrepancies between measures and the prevalence rates as well as the odds ratios of discrepancies depending on sex, age, education and cognitive status. Data are from a nationally representative sample of the Swedish population aged 77 or above (=492). The results show that discrepancies occur among a minority of the sample and with no distinctive bias toward either under- or overestimations of functional ability at the cross-sectional level. Cognitive impairment seemed to increase the risk of discrepancies. Women showed an increased tendency toward discrepancies between measures of upper body function. Age and education showed associations with some discrepancies but were not significant in the multiple regression models. In conclusion, there is a risk of systematic biases in the association between self-assessed and performance-based measures of function. At the cross-sectional level, however, these differences are small.