Some limitations should be carefully considered when interpreting the study results. Since we used cross-sectional data, we rely on the assumption that diseases cause disability. However, this is not necessarily true, although it is plausible [1] according to the disablement model proposed by Verbrugge and Jette [60]. Consequently, diseases may be incorrectly attributed to disability in cases where disability onset preceded disease onset. Also, the use of self-reported data may have resulted in an underestimation of the contribution of diseases, as the validity of self-reported diseases differs according to the diseases being studied [61]. Furthermore, the background contribution to both mild and severe disability might be overestimated due to lack of information of important disability causes, such as injuries and mental disorders [10].