In a television advertisement, a company called "waist away" claimed the workout program on their set of dvds would people lose weight more than any other dvd workout program. to test this claim, an independent company, called "slim down," selected one other dvd program. they then randomly assigned half the volunteers to the waist away program and the other half to the slim down program. each participant was weighed before they started the program and then regularly participated in their assigned program for one month. after one month, each participant was weighed again. the percent of weight lost was recorded for each person, where negative values indicated a weight gain. what type of study was performed?