A researcher conducted a study in which children with problems learning mathematics were offered the opportunity to purchase time with special tutors. The number of weeks that children met with their tutuors varied from 1 to 20. He found that the number of weeks of tutoring predicted mathematics performance in these children and recommended that parents of such children send them for tutoring for as many weeks as possible—for two years if they could afford it. List three problems with that interpretation and explain why each is a problem.