Characteristics of the study samples.

aChi-square and Wilcoxon's rank-sum tests were used to test for between sample differences in categorical and continuous variables, respectively.
b2001 sample N = 366, 2003 sample N = 109.
c%DMA, %MMA, and %InAs, the proportion of total urinary arsenic excreted as dimethylarsinic acid, monomethylarsonic acid, and inorganic arsenic, respectively.
d2003 sample N = 109.
etHcys, total homocysteine.
fDefined as trace protein or greater in urine by dipstick test.
g2001 sample N = 365.
h2001 sample N = 344.
Characteristics of the study samples.

a 分别采用卡方检验（Chi-square test）与威尔科克森秩和检验（Wilcoxon's rank-sum test），对分类变量与连续变量的样本间差异进行检验。
b 2001年样本量N=366，2003年样本量N=109。
c %DMA、%MMA与%InAs分别指代尿中以二甲基胂酸（dimethylarsinic acid, DMA）、一甲基胂酸（monomethylarsonic acid, MMA）及无机砷（inorganic arsenic, InAs）形式排泄的总尿砷占比。
d 2003年样本量N=109。
e 总同型半胱氨酸（total homocysteine, tHcys）。
f 经尿试纸检测，以尿中出现微量蛋白及以上水平为判定标准。
g 2001年样本量N=365。
h 2001年样本量N=344。
研究样本的特征。