What the researchers at Yale performed was a case-control study, an analytic epidemiology method which uses two groups of people: those who do have a disease: cases, and those who don't: controls.

耶鲁大学的研究人员进行的是一项病例对照研究，一种分析流行病学方法，用来比较两组人：那些确实患有疾病的人——病例，和那些没有患病的人——对照组。