A health magazine recently reported a study in which researc

A health magazine recently reported a study in which researchers claimed that iron supplements increased memory and problem-solving abilities in a random sample of college women. All of the women took memory and problem-solving tests at the beginning of the study, then took iron supplements, and then took the same tests again at the end of the study. What is wrong with this design? What confounds could be leading to the results of improved memory and problem-solving skills?

Solution

This design threatens the internal validity of the study. When the same subjects are being tested two times, one without the iron supplement and then with iron they will have a better performance because they have been already exposed to the test. The confounds leading to the results of improved memory & problem solving skills is testing effect. Hence separate samples could be used for the situation.