I just learned of a study analyzing the presence of Walmarts and obesity rates.
You can download the entire paper but at least read the abstract carefully. At one point the author says one variable "explains" the other. But just before that, he says one variable "increases" the other. Claiming that one variable increases another is a much stronger claim than "explains" and largely implies "cause".
Do you think that a causal claim is appropriate? Will building more Walmarts really make people fatter or can something else explain the association?