A Researcher Studied Whether Meeting Regularly with a Weight-Loss Counselor

Multiple Choice

A researcher studied whether meeting regularly with a weight-loss counselor helps dieters lose weight. Eighty dieters were available for the study. Half the dieters, assigned at random, received weight-loss counseling. The other half did not. After six months, the weight lost by each dieter was measured. On the average, those who met regularly with a weight-loss counselor lost more weight than those who did not.
This study is a(n)

A) randomized comparative experiment.
B) experiment, but without randomization.
C) simple random sample.
D) observational study, but not an SRS.