People who finished the course earn more. Cause?
An online education platform reports that students who complete its coding course earn, on average, 20 percent more a year later than students who enrolled but dropped out. It markets this as the salary boost from finishing the course.
Why is completing-versus-dropping a biased comparison, and what would a cleaner test look like?
Your answer
This one is open-ended. Work it through, then check your reasoning against the full solution.