SeattleGriz wrote: ↑Fri Mar 12, 2021 3:17 pm
Recent CDC study shows wearing masks only reduced cases and deaths at MOST 2%, but doesn't account for these other factors.
https://www.cdc.gov/mmwr/volumes/70/wr/mm7010e3.htm
The findings in this report are subject to at least three limitations. First, although models controlled for mask mandates, restaurant and bar closures, stay-at-home orders, and gathering bans, the models did not control for other policies that might affect case and death rates, including other types of business closures, physical distancing recommendations, policies issued by localities, and variances granted by states to certain counties if variances were not made publicly available. Second, compliance with and enforcement of policies were not measured. Finally, the analysis did not differentiate between indoor and outdoor dining, adequacy of ventilation, and adherence to physical distancing and occupancy requirements.
Ok. Finally got to get back to this as my wife's Mom that lived with us passed away in distressing fashion so I had other fish to fry. But here is the deal:
The percent figures apply to case and death growth rates, not numbers of cases and deaths. They calculated percent increase in death rate in a weird way:
The daily growth rate was defined as the difference between the natural log of cumulative cases or deaths on a given day and the natural log of cumulative cases or deaths on the previous day, multiplied by 100.
Just to get a real case rate for illustration, I picked the daily cumulative case count for Wyoming. It's not a county but it's a small State and I had to use something. Anyway, during October, the cumulative case count for Wyoming increased from 5,948 to 13,298. If you assumed there was a constant "percent increase" defined as the authors of the assessment defined it the daily percent increase would be about 2.7 percent.
If you reduce that by 0.5 percentage points, which is the percentage point decrease associated with 1 - 20 days after mask mandates, and so assume that the constant rate is about 2.2 percent, the cumulative number of cases at the end of October drops from 13,298 to 6,079. That's how big a difference what seems like a small percentage point change in the rate makes with the way the authors defined things.
So, no, that assessment does not suggest at all that mask mandates had a minimal effect. It suggests the effect was quite significant in both statistical hypothesis testing and practical terms.
Yes, there are caveats and limitations. It is an observational study. You can't control for everything that might have an effect.
You may not even know everything that might have an effect. All that is handled by randomization in controlled experiments. Unfortunately, as is often the case in public health in general and epidemiology in particular, there is no way to conduct a controlled experiment on the effectiveness of mask mandates.