Do masks work? Debunking the debunker: Pueyo's attempt to debunk Cochrane fails

It is acknowledged that Mr Pueyo is not a scientist and it shows. Cochrane reviews are respected as the best evidence summary in epidemiological research and their practices are clearly scientific.

Mr Puoyo appears to be unaware of the importance of effect sizes, but the Chochrane reviewers certainly were aware. If the effect was so small as to have possibly occurred by chance, the Cochrane reviers did the normal thing and "accepted the nul hypothesis". In this case, if mask wearing could be shown to have only a very small benefit, the Cochrane reviewers rightly concluded that they had no demonstrable effect.

Mr Pueyo's comments are in a long twitter thread here. He gets a lot of things wrong but I will refer to just two of the matters he raises.

1.) About the Aieollo et al study, Mr Pueyo excitedly declares: "The study SUPPORTS masks! But somehow, this Cochrane meta-analysis turns it around"

He totally ignores that the effect concerned was not statistically significant. It was in other words likely a random effect. In science such small effects are accepted as meaning no effect

2.) He also declares of the Abaluck study that "This is the gold standard of mask studies". I agree that it was very good. But what does it show? Again an effect so tiny as not to be accepted as proof of anything: The RR was .87. An RR of 2.0 or more would have been required to be sure that anything real was going on.

I could go on but Mr Pueyo clearly is unfamiliar with normal scientific method. The Cochrane authors WERE following normal scientific procedures in concliuding that there was no evidence to show that masks have any effect. His critique of them fails

A major Covid study which came to the stunning conclusion that face masks were all but useless has been torn to shreds in a scathing take-down.

A recent Cochrane Review – considered the gold standard of evidence-based medicine – assessed 78 high-quality scientific studies, and found “wearing masks in the community probably makes little or no difference” when comparing masking with non-masking to prevent Covid-19.

What’s more, the review found, even for health care workers providing routine care, “there were no clear differences” between medical or surgical masks versus N95s.

The bombshell findings proved controversial, with mask critics seizing on the findings to slam government responses to the pandemic, while supporters argued a different conclusion might have been reached if more and better studies had been available.

But now, Tomas Pueyo – a Silicon Valley executive and writer who made headlines with his detailed modelling of Covid’s spread during the pandemic – has weighed in on the debate, poring over the details and claiming what he found was “so ridiculous it was funny”.

Taking to Twitter, Mr Pueyo – who is not a scientist, but a noted author who analyses “how the world works to shape the future” – said Oxford epidemiologist and the review’s lead author Tom Jefferson’s claim that “there is just no evidence that masks make any difference, full stop” was a “hardcore statement”.

He then broke down the review’s findings to argue his point, revealing there were three groups of studies included.

The first, which covered flu and Covid-like illnesses, found that masks probably work.

The second, which included lab-confirmed flu and Covid cases, found masks increase infections by +1 per cent, and the results for the third lab-confirmed non flu/Covid viruses were -42 per cent.

“But that’s not saying ‘masks don’t work’. That’s saying, ‘We don’t know if masks work.’ Quite a different statement!” he explained.

He then narrowed the findings down further, noting that some studies included in the review were from as far back as the noughties while others included alarmingly small sample sizes.

In one particularly problematic study included in the review, 7700 people out of millions making the Hajj annual Islamic pilgrimage to Mecca from 2013 to 2015 – well before Covid struck – were given free masks and told to wear them for four out of up to six days of the pilgrimage.

Unsurprisingly, that trial was “unable to provide conclusive evidence on face mask efficacy against viral respiratory infections most likely due to poor adherence to protocol”.

However, that clearly flawed study was used by the review to argue that masks increased infections by 40 per cent.

“I mean, they’re technically right on that 40 per cent. That’s what the study recorded. But they couldn’t claim [with] a straight face that masks did that pre-Covid, when nobody had a political opinion about it, or where 2nd order effects (‘mask-wearers are too confident!’) were very unlikely,” Mr Pueyo posted.

Meanwhile, he found that another study, which actually included data collected during the pandemic, found Covid infections were lower by 18 per cent among mask wearers.

He argued the “Cochrane magicians” mixed the studies to claim masks were ineffective by disregarding the original studies’ own conclusions, counting “implausible results”, such as in the Hajj example, and doubling the weight of “convenient” studies.

“If you just go to these primary studies, you realise NONE of them support the conclusion of the meta-analysis. Brutal. If you adjust the math accordingly, you find that there’s just two relevant studies … and both say: MASKS WORK,” he continued.

“In the meantime, it sounds like very flimsy data to make bombastic statements like the one from the lead author of the study … especially since … It’s not what his own study says!”

Mr Pueyo’s criticisms of the review echo those of Australian epidemiologist and biosecurity expert Professor Raina MacIntyre, who told recently there was “overwhelming evidence [masks] work”.

“The Cochrane review combined studies that were dissimilar – they were in different settings (healthcare and community) and measuring different outcomes (continuous use of N95 vs intermittent),” she said.

“This is like comparing apples with oranges.”

Burnet Institute director and CEO Professor Brendan Crabb shared Prof MacIntyre’s views, arguing it would be a “big mistake, a risk to public health” to perpetuate a view that face masks are of little benefit in the battle against Covid-19.

“A randomised controlled trial is not the way to determine real-world effectiveness of these clearly spectacularly successful tools,” he said. Am amazing statement!


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