Fig. 1

Structure of sample by survey year, initial interview year, and survival status at a follow-up wave. (1) Figures shaded in grey were those lost to follow-up. They are excluded from the present study. Figures in italic red font were deceased persons who died before a follow-up, and were also excluded. Figures shaded in yellow were newly recruited samples at a survey. Survivors in a follow-up wave are represented by blue font. (2) The total valid number of individuals who had at least one follow-up interview was 19,070 (=6272 + 5487 + 3249 + 4062)