Socioeconomic status disparities in late-life disability based on age, period, and cohort in Japan.

INTRODUCTION

Effects of disparities in socioeconomic status (SES) on late-life disabilities have been reported around the world. However, there are only a few studies that have examined age, period, and cohort dependent influences of SES disparities on late-life disabilities. We investigated associations between SES disparities and late-life disability based on the Age-Period-Cohort. We also investigated how macro-economic conditions unique to a period, or a cohort might explain the period or the cohort trends.

METHODS

Data were obtained from people aged 65 and over that responded to the Comprehensive Survey of Living Conditions, which had been conducted every three years from 1989 to 2013. SES was assessed via household income. Disability was assessed as disabilities in performing Basic Activities of Daily Living (BADL). Income disparities were evaluated by the slope index of inequality (SII) and the relative index of inequality (RII). Each Age-Period-Cohort dimension was simultaneously controlled using a model for cross-classification of random effects.

RESULTS

Differences in BADL disabilities due to income disparities decreased with age and reversed after approximately 80 years of age. Income disparities in BADL disability changed across periods, by increasing in periods with a high unemployment rate, which started two to four years before the period. Moreover, results of using SII and RII were nearly identical.

CONCLUSIONS

Higher mortality in elderly with lower income might be related to a reduction of income disparities in BADL disability in Japan. Furthermore, exposure to harsh economic conditions might contribute to increased disparities in BADL disability a few years later.