Descriptive statistics of the participants (n = 3293) at enrolment.

1 For categorical variables P-value was obtained from cluster adjusted chi-square tests; for continuous variables from cluster adjusted independent samples t-test. 2 Intra-cluster coefficients Descriptive statistics of the participants (n = 3293) at enrolment.1. 对于分类变量（categorical variable），P值（P-value）通过聚类校正卡方检验（cluster adjusted chi-square test）计算得到；对于连续变量（continuous variable），则通过聚类校正独立样本t检验（cluster adjusted independent samples t-test）计算得到。 2. 组内相关系数（intra-cluster coefficient） 入组时受试者（n = 3293）的描述性统计结果。