There is a lot of extra rigor in a random controlled study than an observational study because it is harder to "cook up data" to support the scientists own beliefs. This may even happen unconsciously.
Instead, it seems more common to establish the "ground rules" of science by some other means, such as arguments about the pros/cons of various scientific methodologies, or even what counts as "scientific methodology" at all (and at this point, you're doing philosophy of science).