Dr. Grodner is conducting an experiment on age-related changes in memory. He is comparing how well retirees and high school students perform on a memory task. In order to conveniently schedule research participants, he has the older adults come to the lab during the day, since they are retired. The students come to the lab in the evening, after they are finished with school and other activities. What is the problematic confound in this study?

The time of day the subjects do the study

Explanation:

In research, a confounding variable refers to an external variable that is not originally taken into consideration and that it changes the effect and relation between the independent and dependent variable.

In this example, Dr. Grodner is conducting an experiment on age-related changes in memory by making retirees and high school students take a memory task. However, the older adults come to the lab during the day while the younger ones come in the evening after they finish their daily activities. We can see that Dr. Grodner is not taking into consideration the variable of the time of the day the subjects come to the lab and that this could be an influence in how well they perform in the task (since the younger subjects might be more tired during the evening) and therefore this would be a confounding variable that would change the results of his study making it not reliable.