An Epidemic of Meta-Analyses – a Veritable Plague?

So says the great John Ioannidis, the world’s leading clinical epidemiologist.[1] He has a point – CLAHRC WM associates Sarah Damery, Sarah Flanagan and Gill Coombes recently published an overview of systematic reviews of ‘Integrated Care’.[2] They over-viewed – wait for it – over 70 individual systematic reviews. But even that number is dwarfed by the 185 systematic reviews of anti-depressants. This might not be a problem (save for waste) if the quality was universally high. Sadly quality is often poor – many (most) reviews are junk. Some are used as a marketing tool and appear to have been manipulated in the service of shareholders rather than patients. Chinese meta-analyses of associations between candidate genes and outcomes are particularly unreliable; they are castles built on sand because the original association studies are so poor. Associations detailed in ‘first generation’ studies were found to be valid in a staggeringly low proportion of less than 2% when compared to multi-centre studies with built-in procedures to preclude selective reporting of data.

The systematic review ‘industry’ seems to be in some disarray. Clearly primary studies need to be improved, although big steps are being made in this regard. Systematic reviews should be done by people without commercial ties to companies whose product is being evaluated. Other ideas are welcome.

— Richard Lilford, CLAHRC WM Director


  1. Ioannidis JPA. The Mass Production of Redundant, Misleading, and Conflicted Systematic Reviews and Meta-analyses. Milbank Quart. 2016; 94(3): 485-514.
  2. Damery S, Flanagan S, Combes G. Does integrated care reduce hospital activity for patients with chronic diseases? An umbrella review of systematic reviews. BMJ Open. 2016; 6: e011952.

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