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We find clear evidence that surgical masks
lead to a relative reduction in symptomatic seroprevalence of 11.2% (aPR = 0.89 [0.78,1.00]; control prevalence = 0.80%; treatment prevalence = 0.71%). For cloth masks, we find an imprecise zero, although the confidence interval includes the point estimate for surgical masks (aPR = 0.95 [0.79,1.11]; control prevalence 0.67%; treatment prevalence 0.62%).
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If you go to the chart, you find a 5% relative reduction with a p-value of 0.540 (!)
Regarding reduction in symptoms:
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Additionally, when we look separately by cloth and surgical masks, we find that the intervention led to a reduction in COVID-like symptoms under either mask type (p = 0.000 for surgical, p = 0.048 for cloth), but the effect size in surgical mask villages was 30-80% larger depending on the specification. In Table A10, we run the same specifications using the smaller sample used in our symptomatic seroprevalence regression (i.e. those who consented to give blood). In this sample we continue to find an effect overall and an effect for surgical masks, but see no effect for cloth masks.
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There's no intellectually honest way to interpret this data other than "cloth masks have very little effect, if any".
--- We find clear evidence that surgical masks lead to a relative reduction in symptomatic seroprevalence of 11.2% (aPR = 0.89 [0.78,1.00]; control prevalence = 0.80%; treatment prevalence = 0.71%). For cloth masks, we find an imprecise zero, although the confidence interval includes the point estimate for surgical masks (aPR = 0.95 [0.79,1.11]; control prevalence 0.67%; treatment prevalence 0.62%). ---
If you go to the chart, you find a 5% relative reduction with a p-value of 0.540 (!)
Regarding reduction in symptoms:
--- Additionally, when we look separately by cloth and surgical masks, we find that the intervention led to a reduction in COVID-like symptoms under either mask type (p = 0.000 for surgical, p = 0.048 for cloth), but the effect size in surgical mask villages was 30-80% larger depending on the specification. In Table A10, we run the same specifications using the smaller sample used in our symptomatic seroprevalence regression (i.e. those who consented to give blood). In this sample we continue to find an effect overall and an effect for surgical masks, but see no effect for cloth masks. ---
There's no intellectually honest way to interpret this data other than "cloth masks have very little effect, if any".