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Accessible Unlicensed Requires Authentication Published online by De Gruyter November 18, 2021

The Impact of Mask Usage on COVID-19 Deaths: Evidence from US Counties Using a Quasi-Experimental Approach

David Welsch

Abstract

I examine the relationship between mask usage and COVID-19 deaths at the county level. When examining this relationship, even the direction caused by the potential endogeneity bias is unclear. In one direction, characteristics that are known to correlate with a larger amount of potential COVID-19 deaths, such as an older population, may make people more likely to wear masks. This will cause a bias that makes mask usage look less effective than it truly is. In the other direction, areas with higher risk tolerances may have less mask usage, but may at the same time be engaging in other behavior that puts them at higher risk for contracting COVID-19. This will cause a bias that makes mask usage look more effective than it truly is. The identification approach exploits a large set of controls and employs percentage of vote for Donald Trump in the 2016 election as an instrumental variable for mask usage. The main finding is that a one percentage point increase in the number of individuals who say they often or frequently wear a mask when within six feet of people will reduce COVID-19 deaths in a county by 10.5%, or six deaths in the average county.


Corresponding author: David Welsch, Professor of Economics, University of Wisconsin - Whitewater, 800 S. Main St., 53190, Whitewater, WI, USA, E-mail:

Acknowledgments

The author would like to thank Nikki Brendemuehl for research assistance. For helpful feedback and comments, the author thanks Benjamin Artz, Jason Baron, Nicholas Lovett, Matthew Winden, and David Zimmer.

Appendix: Additional Tables

Table A1:

First stage results (mask usage frequently/always).

1st Stage 1st Stage
% Vote Trump −0.301*** −0.130***
(0.014) (0.018)
Log per cap. COVID deaths July 1 0.784*** 0.547***
(0.178) (0.172)
Population per 100,000 −0.072* −0.264***
(0.037) (0.048)
Log per cap. All deaths 2016 2.938*** 2.251***
(0.195) (0.202)
% Collegea 0.032
(0.045)
% High school graduatesa −0.038
(0.044)
Percentage minorities 0.138***
(0.017)
Percentage hispanic 0.392***
(0.018)
Percentage female 0.590***
(0.119)
Percentage age 20 to 29b 1.802***
(0.125)
Percentage age 30 to 39b 0.282
(0.215)
Percentage age 40 to 49b 2.722***
(0.206)
Percentage age 50 to 59b 1.566***
(0.203)
Percentage age 60 and overb 1.215***
(0.085)
Average household income (1000s) 0.213***
(0.025)
Population density (square miles) −3.34 × 10−4 ***
(7.59 × 10−5)
F-stat of the excluded instrument 435.07 49.73

  1. All estimations also include a constant. Heteroskedasticity-robust standard errors are in parentheses. *, **, and *** represent significance at the 10%, 5%, and 1% levels, respectively. aThe reference group is % with no high school degree. bThe reference group is % under the age of 20.

Table A2:

Full set of results.

OLS OLS OLS OLS IV IV
(1) (2) (3) (4) (5) (6)
Mask usage frequently/always 0.007*** 0.004*** 0.001 −0.004*** −0.009*** −0.106***
(0.002) (0.001) (0.001) (0.001) (0.003) (0.017)
Log per cap. COVID deaths July 1 0.724*** 0.742*** 0.697*** 0.754*** 0.739***
(0.010) (0.011) (0.010) (0.012) (0.022)
Population per 100,000 0.009*** −0.006** −0.009*** −0.005* −0.034***
(0.003) (0.003) (0.002) (0.003) (0.007)
Log per cap. All deaths 2016 0.078*** 0.076*** 0.119*** 0.328***
(0.009) (0.010) (0.017) (0.048)
% Collegea −0.012*** 7.74 × 10−6
(0.002) (0.005)
% High school graduatesa 6.95 × 10−5 −0.002
(0.002) (0.005)
Percentage minorities 0.012*** 0.033***
(0.001) (0.004)
Percentage hispanic 0.017*** 0.061***
(0.001) (0.008)
Percentage female 0.040*** 0.102***
(0.007) (0.018)
Percentage age 20 to 29b 0.021*** 0.218***
(0.007) (0.036)
Percentage age 30 to 39b 0.004 0.043
(0.011) (0.026)
Percentage age 40 to 49b 0.093*** 0.349***
(0.011) (0.048)
Percentage age 50 to 59b −0.055*** 0.140***
(0.010) (0.040)
Percentage age 60 and overb 0.026*** 0.154***
(0.004) (0.023)
Average household income (1000s) 0.001 0.023***
(0.001) (0.005)
Population density (square miles) −1.10 × 10−5 * −4.08 × 10−5 ***
(6.47 × 10−6) (1.25 × 10−5)
Number of observations 3142 3142 3103 3096 3079 3079

  1. All estimations also include a constant. Heteroskedasticity-robust standard errors are in parentheses. *, **, and *** represent significance at the 10%, 5%, and 1% levels, respectively. aThe reference group is % with no high school degree. bThe reference group is % under the age of 20.

Table A3:

Robustness checks (altering functional form and measures of mask usage).

Per cap Not per cap Not per cap Log per cap Log per cap Log per cap Log per cap Log per cap
Not logged Not logged Logged Between Current Between Mask always only Mask always, freq.,
(1) (2) (3) 7–1 and 9–1 (5) 7 and 1 (7) and sometimes
(4) and current (8)
(6)
Mask usage −0.130*** −1.456* −0.100*** −0.171*** −0.200*** −0.170*** −0.076*** −0.150***
(0.037) (0.744) (0.016) (0.026) (0.047) (0.025) (0.010) (0.026)
COVID deaths 7–1 1.081*** 0.913*** 0.750*** 0.281*** 0.610*** 0.193*** 0.733*** 0.729***
(0.023) (0.022) (0.022) (0.034) (0.059) (0.032) (0.018) (0.022)
Pop in 100,000s −0.017 29.138*** −0.033*** −0.009 −0.149*** −0.020** −0.027*** −0.038***
(0.011) (6.255) (0.007) (0.010) (0.038) (0.009) (0.005) (0.009)
All deaths 2016 0.006 −0.003 0.564*** 0.165** 2.265*** 0.254*** 0.312*** 0.329***
(0.004) (0.008) (0.043) (0.074) (0.139) (0.071) (0.039) (0.051)
% Collegea −0.002 −0.088 4.76 × 10−5 0.005 −0.044*** −0.003 −0.003 −0.004
(0.012) (0.180) (0.005) (0.008) (0.016) (0.008) (0.004) (0.006)
% High sch, gradsa 0.012 0.162 −0.003 −0.007 −0.013 −0.008 0.001 0.007
(0.012) (0.126) (0.005) (0.008) (0.015) (0.008) (0.004) (0.006)
% Minorities 0.081*** 0.420** 0.032*** 0.053*** 0.065*** 0.050*** 0.030*** 0.035***
(0.008) (0.173) (0.004) (0.006) (0.010) (0.006) (0.003) (0.004)
% Hispanic 0.119*** 1.143*** 0.060*** 0.091*** 0.104*** 0.082*** 0.059*** 0.061***
(0.016) (0.237) (0.008) (0.012) (0.021) (0.011) (0.006) (0.008)
% Female 0.254*** 0.968 0.096*** 0.152*** 0.213*** 0.140*** 0.101*** 0.112***
(0.054) (0.761) (0.017) (0.027) (0.051) (0.026) (0.015) (0.021)
% Age 20 to 29b 0.329*** 1.817 0.211*** 0.313*** 0.431*** 0.296*** 0.189*** 0.235***
(0.092) (1.822) (0.035) (0.056) (0.098) (0.053) (0.026) (0.042)
% Age 30 to 39b 0.080 −3.622** 0.042* 0.083** 0.016 0.071* 0.040* 0.044
(0.068) (1.543) (0.025) (0.042) (0.071) (0.039) (0.022) (0.028)
% Age 40 to 49b 0.682*** 4.736** 0.340*** 0.527*** 0.553*** 0.462*** 0.294*** 0.375***
(0.129) (2.014) (0.047) (0.074) (0.134) (0.071) (0.034) (0.057)
% Age 50 to 59b 0.067 1.891 0.126*** 0.195*** 0.221** 0.180*** 0.135*** 0.126***
(0.086) (1.701) (0.038) (0.062) (0.112) (0.059) (0.032) (0.041)
% Age 60 and overb 0.220*** 1.126 0.143*** 0.247*** 0.198*** 0.224*** 0.136*** 0.162***
(0.063) (1.137) (0.023) (0.036) (0.064) (0.034) (0.018) (0.027)
Household income 0.018 −0.324 0.024*** 0.029*** 0.072*** 0.031*** 0.017*** 0.026***
(0.011) (0.290) (0.004) (0.007) (0.013) (0.007) (0.003) (0.005)
Population density −1.61 × 10−4 *** 4.67 × 10−4 −4.13 × 10−5 *** −8.61 × 10−5 *** −7.60 × 10−5 ** −7.88 × 10−5 *** −3.06 × 10−5 *** −4.41 × 10−5 ***
(5.56 × 10−5) (1.68 × 10−3) (1.25 × 10−5) (2.01 × 10−5) (3.39 × 10−5) (1.82 × 10−5) (1.09 × 10−5) (1.33 × 10−5)
1st stage F-stat of excl. IV 68.22 73.33 49.27 49.31 49.73 49.73 84.93 43.29

  1. All estimations also include a constant. Heteroskedasticity-robust standard errors are in parentheses. *, **, and *** represent significance at the 10%, 5%, and 1% levels, respectively. aThe reference group is % with no high school degree. bThe reference group is % under the age of 20.

Table A4:

Reproducing main results with COVID-19 cases. (Dependent variable: Log per capita COVID cases on and before September 1.)

OLS OLS OLS OLS IV IV
(1) (2) (3) (4) (5) (6)
Mask usage frequently/always 0.004*** −0.008*** −0.009*** −0.013*** −0.020*** −0.103***
(0.002) (0.001) (0.001) (0.001) (0.003) (0.015)
0.613*** 0.604*** 0.492*** 0.620*** 0.498***
Log per cap. COVID deaths July 1 (0.010) (0.010) (0.011) (0.010) (0.021)
−0.008*** −0.009*** −0.013*** −0.020*** −0.103***
Population
Log all deaths per capita 2016
Other controls
F-test of exclud. instr. in 1st stage 434.58 47.59
Hausman-WU-Durbin F-stat p-value 0.0000 0.0000

  1. All estimations also include a constant. The estimated coefficients for other controls can be found in Table A2. Heteroskedasticity-robust standard errors are in parentheses. *, **, and *** represent significance at the 10%, 5%, and 1% levels, respectively.

Table A5:

Including social distancing measure as a control.

Mask usage as left-hand COVID-19 deaths as left-hand
side variable (1st stage) side variable (2nd stage)
Mask usage −0.086***
(0.012)
% Vote Trump −0.170***
(0.020)
Social distancing 0.109 0.038*
(0.219) (0.022)
Log per cap. COVID deaths July 1 0.700*** 0.751***
(0.182) (0.020)
Population per 100,000 −0.276*** −0.029***
(0.051) (0.006)
Log per cap. All deaths 2016 2.300*** 0.296***
(0.214) (0.037)
% Collegea −0.010 −0.003
(0.046) (0.005)
% High school graduatesa −0.020 −0.002
(0.046) (0.005)
Percentage minorities 0.097*** 0.028***
(0.018) (0.003)
Percentage hispanic 0.370*** 0.050***
(0.020) (0.006)
Percentage female 0.575*** 0.084***
(0.125) (0.015)
Percentage age 20 to 29b 1.799*** 0.185***
(0.130) (0.028)
Percentage age 30 to 39b 0.271 0.032
(0.225) (0.023)
Percentage age 40 to 49b 2.617*** 0.304***
(0.218) (0.035)
Percentage age 50 to 59b 1.524*** 0.106***
(0.219) (0.032)
Percentage age 60 and overb 1.184*** 0.127***
(0.088) (0.017)
Average household income (1000s) 0.221*** 0.019***
(0.025) (0.004)
Population density (square miles) −3.54 × 10−4 *** −3.41 × 10−5 ***
(8.05 × 10−5) (1.06 × 10−5)
F-stat of the excluded instrument 72.08
Number of observations 2766 2766

  1. All estimations also include a constant. Heteroskedasticity-robust standard errors are in parentheses. *, **, and *** represent significance at the 10%, 5%, and 1% levels, respectively. aThe reference group is % with no high school degree. bThe reference group is % under the age of 20.

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Data Sources

Death data and county population: . Search in Google Scholar

CDC Overall Mortality Data: , . Search in Google Scholar

The New York Times and Dynata Mask-Wearing Survey Data: . Search in Google Scholar

County level presidential election data: . Search in Google Scholar

Social Distancing Data: . Search in Google Scholar

Received: 2021-05-04
Revised: 2021-10-22
Accepted: 2021-10-27
Published Online: 2021-11-18

© 2021 Walter de Gruyter GmbH, Berlin/Boston