To examine the value of looking at old tests, Professor King hands out copies of old tests to the first 20 students who come to class one day. Later she finds that these students got better grades than the other students in the class. What is wrong with this experiment?

Question

Quizplus · Accepted Answer

The experiment lacks random assignment to groups, meaning that the group of students who received old tests could have been inherently different from the other students in the class. This could account for the difference in grades rather than the use of old tests. The other answer choices do not apply to this situation.

To Examine the Value of Looking at Old Tests, Professor