2.4. Statistical analyses
Descriptive statistics were conducted for general characteristics of the environmental exposure and effects. Data with normal distribution were described by mean and standard deviation (Mean±SD), and data with skewed distribution were described by median and interquartile range as M (PIn the linear mixed effect models, the “effective drug” variable is defined as one or more kinds of the effective drug had been taken by the subject (dichotomous variable). The kinds of drug need to be controlled were selected according to Influencing factors of PMThe parameters of the model were tested by bilateral 