evidence: A study from the Centers for Disease Control and Prevention found that state-issued mask mandates were associated with significant decreases in daily COVID-19 case and death growth rates. Yet some conservative outlets and social media users falsely claim the study shows mask mandates have a negligible impact on COVID-19 outcomes. [...] "The data we now have conclusively show that widespread use of masks is a very effective way to reduce the spread of COVID-19," said CDC’s Jasmine Reed in an email. "The CDC study referenced noted that mask mandates were associated with statistically significant decreases in county-level daily COVID-19 case and death growth rates." [...] The new study cites and builds upon previous studies that have confirmed the effectiveness of mask mandates and restaurant closures in reducing COVID-19 outcomes. In this case, CDC scientists examined the association of state-issued mask mandates and on-premises restaurant dining with COVID-19 cases and deaths from March 1 to Dec. 31, 2020. To do so, it looked at data from 2,313 U.S. counties (73.6% of a total 3,142) where mask mandates were implemented and from the 3,076 (97.9%) U.S. counties that allowed restaurants to reopen, and compared that data with county-level changes in COVID-19 case and death growth rates.