From the excellent Fight Aging! blog comes a pointer to "A Histogram of Results from Life Span Studies", a graph of thousands of animal studies by Kingsley G. Morse Jr. (updated version from mailing list):
(This is not the same as a funnel plot, as the y-axis is # of studies finding that percentage gain and nothing to do with the n of studies.)
On the closed GRG mailing list, the compiler says:
Many test the same intervention on a different strain of the same species, or with a different dose.
I asked some questions, and Steven B. Harris replied:
“I was gratified to be able to answer promptly, and I did. I said I didn't know.” (Twain)
Though I can observe that the center of that distribution isn't very far from no-effect, and one would expect that there's a publication bias toward reporting positive effects vs. null effects. I would think that could account for it entirely.
There's also the problem we've discussed before, that feeling animals stuff they don't like the taste off, amounts to calorie restriction. So this clouds the issues terribly in non-CR studies, unless you're very, VERY careful to control them somehow.
The relevance of this summary graph to news like the C60 rodent life extension experiment is obvious. Reading GRG has been interesting and educational about that experiment; a rough summary of points made by various people including myself:
- contradictory median/lifespan figures
- duplicate image
- small sample
- doses of C60 small enough that the direct antioxidant activity can't be responsible
- justifying cites not published when experiment started
- the C60 was administered for brief period (think the analogy given was 'imagine taking a supplement only during your 40s and doubling your lifespan')
- the massive life extension observed in the olive-oil-only rats - not doubling, but still really implausible