Measuring Mask Use Compliance in Shelby County
The School of Public Health highlights change in behaviors based on policies
The University of Memphis School of Public Health conducted research to assist the Shelby County Health Department and the mayor's COVID-19 Joint Task Force in their response to COVID-19. The study, led by Dr. Marian Levy and Dr. Vikki Nolan, used direct observation strategies to examine pre-post trends of compliance with Memphis' city-wide Facial Mask Ordinance and the Shelby County Health Directive enacted on June 25 and July 3, 2020, respectively.
Four public health graduate students observed the number of individuals in public wearing masks correctly (covering mouth and nose) in 20 heavily-trafficked large retail locations (e.g., groceries, home improvement stores) across the county. Site locations were randomly selected by the Shelby County Health Department, with 10 sites being in zip codes with high COVID-19 transmission and 10 in zip codes with low COVID-19 transmission rates. Data was collected via cell phones using a database created in ©2020 Ninox Software.
Observations were conducted at seven intervals in 2020: June 15-21 (pre-policies); July 9-15 (post policies); and at intervals in five subsequent months (Aug. 10-16; Sept. 16-22; Oct. 10-18; Nov. 13-18; and Dec. 4-9). In observing nearly 28,000 individuals (~14,000 pre/post) across Shelby County, researchers found dramatic increases in mask usage following policy implementation.
Before the mask policies, overall mask use (at all 20 locations combined) was 51%. After the mask policies were enacted, overall mask use at these retailers increased significantly to 92%. One-month post-policy implementation, overall mask usage was not only sustained, but increased to 96%. Subsequent observations in the months that followed documented sustained high levels of compliance (95-96%).
Moreover, there was evidence of a clear gradient of increased mask use with age. Pre-policies, usage was lowest among youth aged 2-18 (35%) and highest use among adults over 55 (64%). The age gradient continued over time, but there was at least 90% compliance for all age groups post-policy implementation. Importantly, the gap in compliance between the high and low transmission groups narrowed from 17% pre-policies to 3% post-policies.
Rate of compliance for each race/ethnicity increased over time to over 90% compliance for each group that mostly remained or increased post policies. The Hispanic/Latinx group showed the most dramatic increase, from 34% to 93%. White and Black groups had similar rates of compliance at all-time points, increasing from ~50% pre-policies to ~92% post policies and further increasing to 96% post-policy implementation. Asians had the highest initial rate of compliance (91%) that increased to 96% post policies and returned to pre-policy rate one month post policies. The high compliance rates were sustained in months that followed.
In summary, mask usage increased dramatically for all age, race, and ethnic groups after implementation of the mask policies. The increases were not only sustained but, in most cases, surpassed one month post implementation. These findings were used to determine the effectiveness of the mayor's COVID-19 Joint Task Force strategies to encourage mask usage, as well as to inform communications and policy tactics to improve compliance.
The School of Public Health gratefully acknowledges the support of Dr. Alisa Haushalter (Shelby County Health Department director); Dr. Manoj Jain (consultant to the mayor's COVID-19 Joint Task Force); and Dr. Jeff Warren (Memphis City Councilman). We also appreciate the contributions of Jerelyn Carmichael, Gabby Dowdy, Erick Kalobwe, Rebecca Kronenberg, and the Master of Public Health students who collected the data.