Thread by @dgurdasani1

I've just been reviewing the DfE 'study' that was widely reported in the media as showing 'no evidence masks work in schools'. I honestly can't believe this was even written up into a formal report given the *huge* limitations.🧵

The study compared mask wearing in schools that responded to a question reporting mask use *either in communal areas or classrooms* for just *2 wks* or more- and assessed the impact on absenteeism just 3 wks later!!

Let me unpick this- we don't even know if the schools in the treatment group had kids *wearing masks in classrooms*. Given this was Oct '21 it's very likely that a substantial proportion if not the majority just had masks in communal areas (corridors)!

This is *not* the same thing at all. The researchers did not differentiate the two, despite this being *critically* important. And the duration of the study intervention was *2 weeks* to study the complex intervention of mask use on absenteeism.

On top of all this, it's clear that the schools that had mask policy were completely incomparable to schools that didn't- with a huge difference in distribution of absenteeism at baseline, *even before mask use started*. And they remained different after statistical correction!

While the researchers tried to adjust for this statistically, the difference was so large that it brings the validity of the whole study into question. Amazingly despite this they found a 11% greater relative reduction- with absenteeism dropping more in schools with mask use.

It wasn't statistically significant, which means we cannot rule out that it's a finding that's by chance. But seriously- if you're looking at the impact of mask use in *communal areas or classrooms* for just 2 wks in vastly different groups at baseline - you can't say anything.

Find it amazing that the media and our govt largely ignored the global evidence on mask use in schools, which the DfE report recognises, to report this study (which to be honest wasn't even designed to study the effectiveness of masks in classrooms) as evidence against!

I find it pretty shocking that the DfE would put out something like this - given the massive flaws in this study, and the fact that it's basically designed in such a flawed way that there's no way to interpret it. It's basically useless.

If you do want to know about evidence around masks, and masks in schools, there's loads. Here's a great catalogue of evidence:

https://twitter.com/trishgreenhalgh/status/1414294003479089154?s=20&t=W8I9WbfAKlBxiXC__xsuBg

Here's the DfE report for those interested in delving further:
assets.publishing.service.gov.uk/government/upl…