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12集》

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  I won't talk about that in particular,
  我不会具体介绍这个
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  but I will about cross-sectional studies.
  但是我会讲讲横向研究法
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  There are longitudinal studies, and experimental studies,
  接着也有纵向研究法和实验研究法
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  so let's break those down.
  所以让我们挨个讲解下
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  Cross-sectional studies might look like this,
  横向研究法是这样的
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  where you're taking a snapshot at one point in time
  你们就一个群体
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  of a group of individuals
  开展了一次性调查
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  and you might, if you have enough subjects,
  然后 如果你们有足够多实验对象
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  be able to compare groups of individuals.
  就可以对不同群体进行比较分析
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  Let's say this is a hypothetical example
  举个假设性的例子
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  that looks at cholesterol levels, smoking and heart disease
  我们就不同性别的群体调查
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  in a group of males and females.
  他们的胆固醇水平 吸烟和心脏病情况