Regarding your #3 and the Iowa study, the results do not show what you state. Due to the small numbers in the unmasked/masked group, and in the masked/unmasked group, the confidence intervals are wide (about 3X wider than those for the unmasked/unmasked and masked/masked groups).
Regarding your #3 and the Iowa study, the results do not show what you state. Due to the small numbers in the unmasked/masked group, and in the masked/unmasked group, the confidence intervals are wide (about 3X wider than those for the unmasked/unmasked and masked/masked groups).
The CIs for the unmasked/masked group and the masked/unmasked group (which are the groups I assume you're comparing) overlap. This means that the data presented does not show a difference between the 2 groups. There may be a difference (or there may not be), but the data presented did not show it. It certainly does not "show the best odds of avoiding Covid is if Index patient does NOT wear a mask." You are misinterpreting the results, though it is a common mistake.
To get a better idea of the effectiveness of masks using the CDC data for the Iowa study, examine the data (and, importantly, the CIs) for the 2 groups with the much greater number of cases (more than 9X) relative to the discordant groups.
For those in which both were masked, the results were 12.5 (9.6–16.3); for those in which both were unmasked, the results were 26.4 (22.9– 30.7). Note that the upper limit of the secondary attack rate for those in which both were masked was 16.3, significantly lower than the lower limit of the secondary attack rate for those in which both were unmasked (22.9), and there was no overlap in the CIs. This is consistent with the hypothesis that masking significantly reduces the secondary attack rate.
Thanks for your expansive reply.
Regarding your #3 and the Iowa study, the results do not show what you state. Due to the small numbers in the unmasked/masked group, and in the masked/unmasked group, the confidence intervals are wide (about 3X wider than those for the unmasked/unmasked and masked/masked groups).
The CIs for the unmasked/masked group and the masked/unmasked group (which are the groups I assume you're comparing) overlap. This means that the data presented does not show a difference between the 2 groups. There may be a difference (or there may not be), but the data presented did not show it. It certainly does not "show the best odds of avoiding Covid is if Index patient does NOT wear a mask." You are misinterpreting the results, though it is a common mistake.
To get a better idea of the effectiveness of masks using the CDC data for the Iowa study, examine the data (and, importantly, the CIs) for the 2 groups with the much greater number of cases (more than 9X) relative to the discordant groups.
For those in which both were masked, the results were 12.5 (9.6–16.3); for those in which both were unmasked, the results were 26.4 (22.9– 30.7). Note that the upper limit of the secondary attack rate for those in which both were masked was 16.3, significantly lower than the lower limit of the secondary attack rate for those in which both were unmasked (22.9), and there was no overlap in the CIs. This is consistent with the hypothesis that masking significantly reduces the secondary attack rate.
No, thank you! I rarely get pushback when diving into these studies. Appreciate your thoughtful feedback!