Dr. Sheffield is a clinical psychologist who specializes in treating pathological gambling. Pathological gambling is defined as being unable to resist impulses to gamble. Bothered by not having a good measure that he can give to clients to determine whether they are suffering from this condition, he creates a new measure of pathological gambling. The measure has 15 questions, and it takes 20 minutes to complete. To test his measure, Dr. Sheffield gives his measure to a group of his clients and at the same time measures how many times they have been gambling in the past month. He predicts that clients who score higher on his measure will also report gambling more times in the past month. This procedure is meant to provide evidence for which of the following?