混杂因子是指一个与暴露和疾病都有联系的因子，它既是所研究疾病的独立危险因子，在非暴露组中它也必定是一个危险因子。
解决这一问题的主要方法是将混杂因子作为分层变量把被研究群体分层。
The main approach to solve this problem is to stratify the population studied through taking the confounder as the stratifying variable.
在调整潜在混杂因子的影响后，相应的患病风险下降率下降到28% - 32%。
After adjusting for potential confounding factors, the corresponding risk reductions fell slightly to 28% and 32%.
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