And you're not trying to get at causality. And in a sample study, a sample study, this is just you trying to estimate a parameter for the entire population. So a sample study might have been of the entire population, what percentage gets migraines? And you can't talk to the entire population, maybe the entire population is millions of people, so you take a sample of, say, 100 people, and you ask them, do you get migraines? And then you say, okay, that percentage of our sample that get migraines, that's a good estimate for the parameter of what percentage of my entire population actually gets migraines. So this was clearly an experiment. Now the next question is, was this experiment conducted well?