受试者按年龄、性别及其他人口统计指标进行匹配分组，他们中无吸烟者，无糖尿病、心血管疾病、癌症、肺部及其他慢性疾病。
The subjects were matched for age , sex and other demographic factors , and no one smoked or had diabetes , cardiovascular disease , cancer , lung disease or other chronic illness .
人口统计指标