Dr. DeVries is interested in measuring how practice in problem solving affects this ability. The population of interest is high school seniors, and the sample consists of students who attend an exclusive college preparatory school. Half of the sample receives practice in solving particular types of problems, while the other half does not. Both groups take the same problem-solving test. Which of the following might best explain why Dr. DeVries may not be able to generalize his findings?a.He is not taking into account how the scores on the test might deviate from one another.b.His data may be positively skewed.c.He should have conducted his experiment in a lab instead of a natural setting.d.His sample is not representative of the population.e.He did not receive approval from an Institutional Review Board (IRB) before beginning his research.

Explanation: Dr. DeVries should choose his sample population randomly in order for his research to be representative, even having a specific population, which is high school seniors, that he wants to study. By choosing specifically students from an exclusive college preparatory school, he isn't considering how students from other schools might perform in his research test. This would be a very important step for him to understand how the practice in problem solving affects the ability related to it. Otherwise, he will have a distorted result.