Baseline characteristics of the COPD patients in the study sample categorized by measured levels of serum vitamin D (25(OH)D) and Vitamin D binding protein (VDBP).

* ttest for age, chi square for all other variables** ANOVA for age, chi square for all other variabels.Baseline characteristics of the COPD patients in the study sample categorized by measured levels of serum vitamin D (25(OH)D) and Vitamin D binding protein (VDBP).

* 针对年龄行t检验，其余变量行卡方检验** 针对年龄行方差分析（ANOVA），其余变量行卡方检验。本研究样本中按血清维生素D（25(OH)D）与维生素D结合蛋白（VDBP）检测水平分组的慢性阻塞性肺疾病（COPD）患者的基线特征。