One of the difficulties of implementing effective health policy is that it is so hard to study. You're learning about a few "natural" experiments in health policy this week and one of the largest-scale health policy research efforts to date. Most interventions have a period of performance where we test how well it's working, assess, and revise. But we don't do that for federal and state policies that often, and rarely in healthcare. What would a system where all policies have to be evaluated look like? What are the pros and cons of such a system?