Dr. Stevens wants to examine the relationship between body mass index (BMI) and depression. He selects as his research subjects a sample of American athletes who are currently training for the summer Olympic Games. Dr. Stevens finds no relationship between BMI and depression. Which of the following is one problem with his research design that could have kept him from finding a relationship between those variables?

Restriction of Range.

Explanation: In most research studies such as statistical analysis to delineate the correlation or relationship between variables, choosing subjects to be used in the experiment remains of paramount importance. Once the chosen sample to be used in the experiment isn't representative, then we already have a failed experiment.

Dr. Steven's research sample choice exhibits a RESTRICTION OF RANGE PROBLEM whereby sample does not cut across the entire range or category of variables required to establish a meaningful relationship, hence the sampling population has been shortened or condensed.