Dr. Bruno was interested in the effect of praise on performance. He randomly assigned subjects to either a group that received praise or a group that did not receive praise. For the high praise group, Dr. Bruno gave them encouraging feedback regardless of whether they solved the problem correctly. For the group that did not receive praise, he simply told subjects "Your time is up, go on to the next problem" after each problem. In addition, he manipulated task difficulty by having each subject in the experiment solve both a set of 30 hard and a set of 30 easy math problems. Half the subjects started with the hard problems, got a 15 minute break, and then went on to the easy problems. The other half started with the easy problems, got a 15 minute break, and then went on to the hard problems. The design of Dr. Bruno's study is The design of Dr. Bruno's study is 2 x 2 between-subjects factorial design 2 x 2 quasi-experimental factorial design 2 x 2 mixed subjects factorial design one-way factorial design with two independent variables Pretest-posttest design