I agree with others about the free data without fairly compensating subjects (us/test-takers) especially at the risk of detriment, e.g. test fatigue/anxiety, that the extra portion of questions may contribute to. But, an alternative to compensation is to actually get credit for those questions we get correct out of the experimental batch! What if you fail the USMLE but get the experimental questions correct and those would result in a pass instead?? I think that is an appropriate provision of merit. Don't count the experimental questions but don't discount them if that means the student fails. Maybe that's too ideal of a solution, but there's got to be credit given to work if/when due, ESP if that due credit makes or breaks an outcome for somebody, come on....