I think it helps a lot if you have a plausible explanation for the chain of causes. For example, the correlation of dead people in houses with shitty stoves and furnaces in those houses is interesting, but once you discover that said stoves and furnaces leak carbon monoxide, AND that carbon monoxide binds to hemoglobin with much greater affinity than oxygen, AND that the affected people don't receive any specific warning symptoms when that happens, you suddenly have a reason to stop wondering whether or not they were committing suicide at a heightened rate because of poverty-related depression.

It depends where the data comes from. The gold standard in science is a controlled, randomized experiment - but obviously that standard is not always attainable.