onstrated using studies that experimentally control and manipulate a specific factor. In medicine, such a study is referred to as a <em>randomized controlled trial</em> (RCT). Let’s say that we wanted to do an RCT to examine whether increasing saturated fat intake increases life span. To do this, we would sample a group of people, and then assign them to either a treatment group (which would be told to increase their saturated fat intake) or a control group (who would be told to keep eating the same as be