And you know that the effect can't be "anywhere near 76%"? On the basis of what do you claim to know these things?
I was ready to argue with you on this, because jimrandomh seemed to be applying a sensible heuristic here, namely: discount exaggerated reports of a study that say you can massively cut your risk of a chronic disease by doing an arbitrary thing. Normally there are only a few lifestyle factors that have such big effects: smoking, drinking, exercise, and diet. Maybe stress.
But of course frequent dancing is regular exercise. So, on reflection, the true causal effect could be on the order of 76% (though probably less). However, I predict it won't be substantially more than the true causal effect of regular exercise in general.
I don't agree with your general point; just because a claim isn't explicitly justified doesn't mean it has "no backing at all". I would happily pooh-pooh double-blinded, placebo-controlled studies concluding that acupuncture can cure AIDS, even without "backing" my pooh-poohing, because it just isn't plausible that acupuncture can cure AIDS and most people should have that as background knowledge (or at least be able to deduce it).
Still, we're hardly talking about acupuncture & AIDS, so in this case your questions are fair. Dancing is exercise, exercise can have big preventive effects on chronic disease, and dementia is a chronic disease. Maybe dancing can reduce dementia risk a lot. I think an anti-halo effect from the sloppy argument in NancyLebovitz's link made people underrate the hypothesis' prior probability.
But of course frequent dancing is regular exercise. So, on reflection, the true causal effect could be on the order of 76% (though probably less). However, I predict it won't be substantially more than the true causal effect of regular exercise in general.
From the study: "The physical-activity score was not significantly associated with dementia, either when analyzed as a continuous variable or when the study cohort was divided into thirds according to this score "
Frequent dancing causes a 76% reduction in the risk of dementia. The benefit seems to be from freestyle social dancing, though I don't think that part is as well-verified. The benefit seems to be from making large numbers of quick decisions.
I wonder if playing jazz has similar good effects.
For something a little geekier, Shiva Nata, a system of keeping the mind fresh by doing more and more complex movements. The author of the blog is a silly person, but the system seems to be for real.
Edited to correct html which was entered in the text field instead of the html field. It wouldn't surprise me if having to deal with electronics and computers tends to prevent dementia, considering the number of fiddly and changing details one has to deal with. Or is fun required?