Factors explaining disability-free life expectancy in Japan: the proportion of older workers, self-reported health status, and the number of public health nurses.
BACKGROUND
Disability-free life expectancy (DFLE) data for 47 prefectures in Japan were reported in 1999; however, few studies have identified the factors associated with the length of the DFLE. The objective of this study was to elucidate the primary factors that explain differences in DFLEs in Japan.


METHODS
In our ecological study, 47 prefectures in Japan were used as units of analysis. The DFLEs for men and women at 65 years of age (DFLE65), calculated by Hashimoto et al using Sullivan's method, were set as dependent variables. From various national surveys, 181 factors associated with demographics, socioeconomic status, health status and health behaviors, medical environment, social relationships, climate, and other areas were gathered as independent variables. Pearson's or Spearman's correlation coefficients were calculated to screen independent variables potentially associated with the DFLE65s. Then, multivariate linear regression analyses were conducted for the selected 24 independent variables after adjusting for the proportion of older people (65 years or more) and population density.


RESULTS
Multivariate linear regression analyses revealed that the large number of public health nurses per 100,000 population, a good self-reported health status, and a high proportion of older workers were significantly associated with long DFLE65s for both genders.


CONCLUSIONS
These three factors could potentially explain the differences in DFLE of the older population in Japan.
Kondo
Naoki
N
Department of Health Sciences, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, 1110 Shimokato, Tamaho, Nakakoma, Yamanashi, Japan. nkondo@yamanashi.ac.jp
Mizutani
Takashi
T
Minai
Junko
J
Kazama
Mari
M
Imai
Hisashi
H
Takeda
Yasuhisa
Y
Yamagata
Zentaro
Z
D000368:Aged; D005260:Female; D015577:Geriatric Assessment; D006304:Health Status; D006801:Humans; D007564:Japan; D008017:Life Expectancy; D016014:Linear Models; D008297:Male; D011637:Public Health Nursing / Q000706:statistics & numerical data*; D012923:Social Class