A group of kinesiology students wanted to know if individuals who took group fitness classes lost more weight than individuals who worked out on their own. They obtained a sample of 70 individuals who wanted to lose weight. The first 35 participants to show up for the study were assigned to the group fitness condition; they attended a group fitness class twice a week. The second 35 participants were assigned to the individual workout condition; they worked out alone in the gym twice a week. Change in weight over a 15 week period was recorded and compared for the two groups.

Is this an observational or experimental study?