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?a. There is a third-variable problem.
b. There is a restriction-of-range problem.
c. There is a problem with outliers in his sample.
d. There is a directionality problem.