Exactly. Plus, we need to hold all other variables equal, so we can be sure what the causation is. And best of all we should use the gold standard, randomized

Exactly. Plus, we need to hold all other variables equal, so we can be sure what the causation is. And best of all we should use the gold standard, randomized controlled trials. With this method, some states/countries get randomly selected to implement a policy, but they don't even know about it, and to make it double blind, we also don't know about it until after the trial. Anything less is unscientific, frankly.