Fig. 2

CESD by each nine SRH-combined categories, by income quartile groups from low to high consequence. CESD means the center for epidemiologic studies depression scale, which is a screening test for depression and depressive disorder. Among the low SRH-global * low SRH-age group [LL], all estimates of CESD had positive value compared to the reference group with statistical difference and the beta estimates were increased as the income was increased (low; beta = 0.433, p < 0.001, middle-low; beta = 0.788, p < 0.001, middle-high; beta = 0.823, p < 0.001, high; beta = 1.011, p <0.001). Interestingly, only the middle-low quartile group in the middle SRH-global * the low SRH-age ([ML], b = 0.478, p = 0.013) and the high SRH-global * the low SRH age ([HL], b = 0.946, p = 0.001) categories showed statistically differences. *P < 0.05, **P < 0.001