Technically they state an “odds ratio of 0.82 (CI of 0.54 to 1.23)”. So their “mean” would be about 18% (1-0.82) reduction in risk of infection. When talking odds ratios, the mean isn’t always perfectly centered between the CI upper and lower limits.Ok, thanks. So would the mean then be an 11.5% decrease among mask wearers?
BUT, we should note they didn’t find this to be “statistically significant”, which means we can’t say for certain that this result wasn’t just due to chance. So in the future someone would maybe try and repeat this study with a larger sample size, to see if this finding is significant. This study specifically asked the question, “does wearing a surgical mask reduce risk of infection by 50% or more?” Their results suggest no, it doesn’t reduce risk that amount.