But if we compare California to Florida/Texas, for example, we can at least say pretty conclusively though that the effect wasn't strong enough to overcome climate differences or whatever other confounding variables might be involved. So while we can't say for sure they aren't effective at all, we can place a limit on how effective they are based on the data, and as far as I'm aware, that points to them being marginal at best. They certainly aren't, in themselves, any kind of panacea for stopping a pandemic--that much has been proven.