because the same group of people are followed over time.

因为一直都是对同一群体进行追踪
You'll see longitudinal studies, cross-sectional studies

在我要求你们阅读的论文中你将看到
mixed in to the sort of papers that I'm having you read.

其中混合了纵向和横向研究
It's interesting for you to think about

有意思的是你可以想想
what you--what it means when it-- in the abstract of a paper it says,

论文摘要说的这是一个纵向横向对比研究
this is a longitudinal cohort study versus a cross-sectional study.

到底是什么意思
Here's an example. Let's take a study and interpret this.

这有个例子我们一起学习并解释下
2006 there was a paper published

这篇论文2006年发表于
in The Journal of the American Medical Association

美国医学会杂志上
looking at green tea consumption,

着眼于绿茶的摄入量
the mortality due to cardiovascular disease

与心血管疾病的死亡率的关系
in a Japanese sample of individuals.

个体样本来自日本