Distribution of baseline characteristics of the study population by secondhand smoke exposure. Numbers presented are count (percentage) unless otherwise specified.

*Residing in a crowded home: more than or equal to eight persons per household.**Never-not current users of alcohol; social-less than once a week; regular-once a week or more and not to the extent of being intoxicated; heavy-once a week or more and to the extent of being intoxicated.* 居住于拥挤家庭：每户家庭成员不少于8人。** 饮酒分层标准如下：从不饮酒（即非当前饮酒者）；社交性饮酒：每周饮酒少于1次；规律性饮酒：每周饮酒1次及以上，但未达到醉酒程度；过量饮酒：每周饮酒1次及以上，且达到醉酒程度。