Meta-analysis really is just a simple statistical aggregation of results. Indeed, the most basic way to meta-analyze studies is just to use a mean or median of their point-estimates
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But simple means/medians can be misleading - we don't really want a study of 10,000 to have the same weighting as a study of 10, but that's what a simple average provides
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When we run a meta-analytic model, what we are actually doing is generating a WEIGHTED mean/median, and confidence interval. Essentially, we take all of the means and SEs, and based on that our model weights them with bigger studies generally contributing more to the modelpic.twitter.com/8WrRkjVflu
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You'll notice I've said nothing about the underlying quality of the evidence That's because META-ANALYSIS HAS NOTHING TO DO WITH QUALITY OF EVIDENCE
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You can throw anything into a meta-analysis model. Here's a model I just ran on the ratio of hosting to participating in the summer Olympics. This is meaningless!pic.twitter.com/snEmahYVDg
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We tend to put meta-analyses on a pedestal, but the fact is that statistically aggregating evidence is a total waste of time if that evidence is all bad
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Health Nerd Retweeted Health Nerd
This recent Cochrane review is a perfect example - they looked at the evidence for ivermectin for COVID-19, but because most of it was terrible they only included a few studies in their modelhttps://twitter.com/GidMK/status/1420340231786549253?s=20 …
Health Nerd added,
Health NerdVerified account @GidMKCochrane review on ivermectin just dropped. This is the current gold-standard summary: "the reliable evidence available does not support the use ivermectin for treatment or prevention of COVID‐19 outside of well‐designed randomized trials." https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD015017.pub2/full …Show this thread6 replies 12 retweets 60 likesShow this thread -
This is also where the phrase "garbage in, garbage out" comes from. If your meta-analysis includes numbers from studies that are terrible, the final point estimate is as meaningless as my graph above on the Olympics
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Some people think meta-analysis is impressive because it involves fancy statistical software, but it's entirely possible to implement a Dersimonian-Laird inverse-variance model in Excel with a stats textbook and a few hours of time
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Replying to @GidMK
So I think a more accurate statement is that meta-analysis highly weighted by low quality research is valueless. This might be better than saying meta-analysis is useless. No need to contempt meta-analysis as a method itself.
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Meta-analysis is a simple aggregation of data, and thus is only as valuable or valueless as the underlying research. Gold-standard clinical trials systematically reviewed -> high-value meta-analysis
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