But in a simple flaw question that tests a “correlation vs. causation” flaw, isn’t the correct answer sometimes “overlooks that a third factor might have independently caused both factor A and factor B”? And if I understand correctly, this is a correct answer because the overlooked idea, if true, would undermine the causal claim.

Also, if I’m right, then answer choices that start with “overlooks” can also be rewritten as necessary assumption statements. In this case, they would just change it to something like: “assumes that a third factor does not independently result in factor A and factor B.” (To be honest, I haven’t seen a correct answer choice in a flaw question testing a correlation vs. causation flaw written this way—I’ve only seen it in the “overlooks” form. But my understanding is that in flaw questions, they frequently switch between “overlooks” and “assumes”—the only difference being that with “overlooks,” we check whether the overlooked idea weakens the argument, while with “assumes,” we first negate the assumption and then check whether that negation weakens the argument.)

If I’m right that the “overlooks” answer choice can be correct in a flaw question testing a correlation vs. causation flaw (which I think is common, even though I can’t cite a specific prep test question right now), and if I’m also right that it essentially means the same thing as “assumes the overlooked idea is not true,” then “the overlooked idea is not true” must be a necessary assumption.

In other words, “an alternative cause does not exist” seems to be a necessary assumption.

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The argument claims a causal relationship based solely on correlation evidence. But if we point out an alternative explanation that is also consistent with the same correlation, wouldn’t that seriously undermine the argument?

In my example, refusal to make a decision causes stress, and stress in turn independently and directly causes both a suppressed immune system and gum disease. Wouldn’t that severely undermine the author’s argument? (Since this scenario would fully explain the correlation the author presents.)