Yaneer Bar-Yam

New paper: Masks in schools

30% more cases in areas without masks.

Study compares Boston suburbs with Boston & neighboring Chelsea which kept mask mandate longer and had fewer cases — and have older school buildings in worse condition, more students per classroom, low-income students, students with disabilities, English-language learners, Black and Latinx students and staff.

Lifting Universal Masking in Schools — Covid-19 Incidence among Students and Staff

https://www.nejm.org/doi/full/10.1056/NEJMoa2211029?query=featured_home

Lifting Universal Masking in Schools — Covid-19 Incidence among Students and Staff | NEJM

Original Article from The New England Journal of Medicine — Lifting Universal Masking in Schools — Covid-19 Incidence among Students and Staff

New England Journal of Medicine
Nov 11, 2022 at 1:21amWeb
Show threadYaneer Bar-YamNov 11, 2022
Note that the paper used a "Difference-in-difference" method to compare the trends of the two different areas relative to what was happening before in those areas. This provides a way to adjust for underlying differences between regions.
Show threadYaneer Bar-YamNov 11, 2022

Important correction: The difference beteen the schools without and with masks was a factor of 2X: 100% increase. See the table attached.

The 30% was comparing the extra cases to all of the cases in the area not one relative to the other.