Let's say you want to see how something like cigarette smoking is changing in the population and the rates of cigarette smoking, and you want to look at people every five years from 1970 to 2000.

比如你想知道,人群中吸烟者的人数变化,和吸烟者的比例,在1970年至2000年每五年的情况

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选