A simple survey of Ryerson freshmen asks students to report how many hours per week they spend studying outside of class and then at the end of the year records their first year GPA. From looking at the resulting data, students who report studying more than 10 hours per week have first year GPAs that are 0.67 points higher than those students who report studying less than 10 hours per week. Why does this survey evidence not necessarily prove that studying leads to higher grades? Before spending resources promoting a pro-study campaign or establishing a more pro-study atmosphere, Ryerson administrators want stronger evidence of the effect of studying on grades. As a public policy researcher, what might you suggest as an approach to produce this evidence?