To show that studying philosophy causes improvement, at least we need to compare them with a control group whose average SAT scores before going to college are

To show that studying philosophy causes improvement, at least we need to compare them with a control group whose average SAT scores before going to college are similar to philosophy majors. Otherwise, it could just be a selection bias (i.e., those who choose philosophy tend to score high on those measures like Verbal and Analytical Writing). Any such studies?