Fig. 1

Dose–response relationship of long-term exposure to air pollution and incident major depressive disorder (MDD). Multiple-adjusted hazard ratio (HR) for continuous air pollution is modeled using restricted cubic splines. Models are adjusted for age, gender, ethnicity, education level, employment status, household income, and Townsend deprivation index. The reference group is considered the minimum exposure level of air pollution in the entire population. Gray bars represent the distribution of the exposure levels in the entire population. The blue solid line indicates HR and the shaded area indicates a 95% confidence interval