来自《耶鲁大学开放课程：有关食物的心理学、生物学和政治学 第4集 第4集》

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  One are epidemiology studies
  一种是流行病学研究
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  and then the second are intervention studies.
  另一种是干预性研究
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  Now the epidemiology studies are observational studies.
  流行病学研究是观察性研究
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  You're not intervening with people,
  不干涉他人生活
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  you're observing usually large numbers of people in a population.
  只是观察一个人群中的许多个体
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  You measure health and you measure a factor like diet,
  你衡量其健康及饮食
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  you measure other factors that might be related as well.
  还有很多其他可能有关的因素
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  So factors such as exercise, or smoking, or other things like this
  所以像运动 吸烟等相关因素
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  that are relevant will be measured
  都需要衡量
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  and then the scientists will look at the impact of something like diet on health
  然后科学家控制其他因素不变
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  while controlling for the other factors,
  以观察某一因素如饮食对健康的影响
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  controlling for the impact of the other factors,
  对其他的影响因素进行控制