Treatments and population growth mean more people than ever are living with H.I.V.

VOA: special.2009.12.02

We can define it in a couple of different ways depending on whether we're talking about sample mean or population mean.

我们有几种不同的方式去定义这个概念,取决于我们指的是,样本均值还是总体均值

耶鲁公开课 - 金融市场课程节选

Well, a cross-sectional study would mean that you'd get a random group of the population and measure them in 1970 and then take another random group five years later and measure them, but it wouldn't be the same people necessarily, it would be different groups of people.

那么,横断面研究就是,1970年你在人群中随意选择一组人,并记录下相关数据,然后,五年后再随意选择一组人记录数据,但这不需要是同一组人,通常是不同的人

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选

Mr.Perry says this does not necessarily mean their population is dropping.

VOA: special.2011.03.14

The population mean is often written "X-bar."

总体均值一般写作X拔

耶鲁公开课 - 金融市场课程节选