In their book SuperFreakonomics, authors Steven Levitt and Stephen Dubner describe the research of behavioral economist John List. List recruited customers and dealers at a baseball-card show to participate in an experiment in which the customer would state how much he was willing to pay for a single baseball card. The prices ranged from $4 (lowball) to $50 (premium card). The dealer would then give the customer a card that was supposed to correspond to the offer price. In this setting, the dealer could certainly give the buyer a card worth less than the offer price, but this rarely happened. The card received by the buyer was close in value to the price offered. Next, List went to the trading floor at the show and again recruited customers. But this time the customers approached dealers at their booth. The dealers did not know they were being  atched. The scenario went something like this: as the customer approached the dealer’s booth, he would say, “Please give me the best Derek Jeter card you can for $20.” In this scenario, the dealers consistently ripped off the customers by giving them cards worth much less than the offer price. In fact, the dealers who were the worst offenders were the same dealers who refused to participate in List’s study. Do you believe that individuals who volunteer for experiments are scientific do-gooders? That is, do you believe that in designed experiments subjects strive to meet the expectations of the researcher? In addition, do you believe that results of experiments may suffer because many experiments require individuals to volunteer, and individuals who are not dogooders do not volunteer for studies? Now, explain why control groups are needed in designed experiments and the role they can play in neutralizing the impact of scientific do-gooders.