A manufacturer of a new diet pill sponsored a study to determine the effectiveness for reducing peoples weight. Three hundred out of 20,000 college students in a large city were paid to participate as subjects in the study. The three hundred participants were selected based on information given about their weight provided by a form they filled out to be part oftche study. All of the selected participants were rated as being overweight at the beginning of the two month study. The subjects were given the diet pill once a day for two months. At the end of the study 227 of the participants provided information that they lost weight over the two months. List three possible causes other than the effectiveness of the diet pill that could have confounded the results of the study. ) The volunteers were paid to participate. College students may not be typical of the population at large in several critical aspects (age, health, etc.). The manufacturer sponsored the study. The participants determined their weight loss. Only three hundred participated from the population of 20,000 students