We are all participants in the only possible conclusive trial of masks
The only evidence we’ll have for the impact of face masks will only ever come from natural experiments, as we all start to wear masks in public.
Like many other countries, England is about to conduct a natural experiment of face coverings in public places.
This is despite the constant bickering of scientists, citing lack of conclusive proof that wearing masks impacts on the transmission of Covid-19.
The trouble is that randomised trials were developed to test drugs, and the scientists involved in the mask debate are mostly medically trained and won’t prescribe without them.
But randomised trials in this situation are impossible. How would you test if my mask protects you and yours protects me, or find a control group, or get enough people in any sample group to give informed consent?
So scientists have only been able to test the effect of mask wearing on the wearer and we have no facts from randomised controlled trials of source control in Covid-19.
In public health, interventions are usually introduced pragmatically and evaluated as before-and-after natural experiments. There are no randomised controlled trials in social distancing, hand washing or closing schools for example. Public health scientists value natural experim
ents highly because they view the trade-off between real-world achievability and experimental ideals as worthwhile.
If transmission rates of Covid-19 fall as a result of wearing masks in public, as predicted, public health experts will say that face coverings are effective source control. But triallists will still clamour for robust evidence.
We are all part of that natural trial and will welcome its inevitable positive results.
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