My bad, I read “confidence” and put “certainty” in their mouth. I can agree other already understood factors exist, and may confound the problem. But confoundin

My bad, I read “confidence” and put “certainty” in their mouth. I can agree other already understood factors exist, and may confound the problem. But confounding != negation. And the health effects of air pollution are well understood and bad enough that denying the link from pollution -> depression is equivalent to denying link from bad health -> depression.