Instead of looking at a group of people who had already caught the disease, we could perform an analysis by finding a group of people and see who goes on to catch a disease, and then study their exposures.

我们可以通过找到一群人来进行分析，看看谁会继续感染疾病，继而研究他们的暴露情况，而不是观察一群已经感染疾病的人。