Test for nonlinear association between MEQ-5 scores and
Depressive symptoms
In addition, we examined the non-linear dose-response relationship
between chronotype (MEQ-5 score) and risk of depressive symptoms by
restrictive cubic splines, as shown in Figure 2. After adjusting for
age, sex, annual income, education, passive smoking, physical activity,
living children, infertility treatment time, cause of infertility,
frequency of insomnia, nocturnal wake frequency, daytime napping, social
jetlag, and nighttime sleep duration, we found that the odds of
depressive symptoms appeared to decrease with increasing MEQ-5 scores
(P overall < 0.001); however, no nonlinear trend was
observed (P non-linear = 0.526) (Figure 1 ).