Unexpectedly Intriguing!
16 December 2020

This is the last time we're going to look at Arizona's experience with COVID-19 in 2020, so we thought it was a good time to answer some questions that have been hanging out for a while. Let's get right to it!

What effect did the Thanksgiving holiday have on Arizona's COVID trends?

This is a question we've been waiting for the data to fill in for a couple of weeks, where it is now complete enough to tell the answer is: None.

If the high volume of social mixing anticipated during the Thanksgiving holiday was going to change the trajectory of COVID-19 cases, hospitalizations, and deaths for the worse, as was feared, we would see an upward shift in the trends for these statistics starting as early as 10 days after the event.

Instead, we see the Thanksgiving holiday affected when people were tested for COVID-19 infections, which creates some noise in Arizona's data for confirmed cases. But aside from that holiday-related anomaly, we've seen no meaningful change in the trend that began with the political campaign events taking place in the state during the period of 23-25 October 2020.

But don't take our word for it. We have four charts to back that assessment up (newly confirmed cases, new hospital admissions, ICU bed usage, and deaths), where only the chart for Arizona's COVID-19 deaths does not yet confirm that observation. And that's only because it takes so much longer for the coronavirus-related deaths associated with a given event to take place and be reported.

Arizona: Newly Confirmed COVID-19 Cases by Sample Collection Date, 30 March 2020 - 14 December 2020
Arizona: COVID-19 New Hospital Admissions, 30 March 2020 - 14 December 2020
Arizona: COVID-19 ICU Bed Usage, 30 March 2020 - 14 December 2020
Arizona: COVID-19 Deaths, 30 March 2020 - 14 December 2020

Has mask wearing made a difference?

The short answer is: Apparently yes. We have two periods where we can compare a non-mask-wearing period with a mask-wearing period. The non-mask-wearing ran from 25 May 2020 through 2 July 2020, which covers the period of time from 10 days after Arizona lifted its stay-at-home order on residents and allowed most businesses to reopen following its initial lockdown order until 13 days after when Governor Doug Ducey issued an executive order allowing counties and local governments to require masks and set other operating restrictions on businesses. During this period, the number of new COVID-19 infections in Arizona was rising by an average of 62 cases per day. Here's the chart for cases again.

Arizona: Newly Confirmed COVID-19 Cases by Sample Collection Date, 30 March 2020 - 14 December 2020

The second period ran from 3 October 2020 through 1 November 2020, which corresponds to the period 10 days after when most of the operating restrictions Governor Ducey had imposed on high-exposure risk businesses at the end of June 2020 were lifted in most counties in the state to 10 days after the October 2020's political events that increased the rate of incidence of new infections in Arizona.

During this second period, Governor Ducey's executive order allowing counties and local jurisdictions to require mask wearing and to set other operating restrictions on businesses has remained in effect. Consequently, in places where 94% of Arizonans live, the rate of mask-wearing compliance has remained high, but with businesses operating at levels similar to what they did following the state's initial lockdown period. During this period, the rate the number of new COVID-19 infections in Arizona was rising by an average of 31 cases per day, half that of the period prior to counties and local governments being able to require masks be worn (this is shown as the "Post-Event H Trendline" on each chart).

The reason the answer to this question is not simply "Yes" is because mask wearing is not the only restriction that local governments implemented. They've also set capacity limits, required protective shields to protect business employees from potentially infected customers, and have mandated other measures that also would have an impact in addition to requiring the public wear masks while at businesses. All of which muddies the water for clearly determining if mask wearing is the primary influence in reducing the rate of new infections.

The most honest answer we can give with the available data is that mask wearing along with these other restrictions do make a difference.

What caused Arizona's uncontrolled surges in coronavirus cases?

The simplest answer is: Political activism. We've previously covered the deadly impact of Arizona's anti-police protests, but the impact of political campaign events in the state before the 3 November 2020 elections cannot be understated since larger numbers of people were involved, which you can see in the charts as the difference between the trajectory of COVID-19 cases, hospital admissions, ICU bed usage, and deaths and the "Post-Event H Trendline" shown on each. This assessment applies across Arizona and across political parties, where counties that went for Biden have been hit hard with surging coronavirus infections, just as other counties have that went for Trump or that were split between both presidential candidates.

The data suggests the best advice we can give to anyone seeking to avoid becoming infected with the SARS-CoV-2 coronavirus is to avoid any personal contact with political activists.

Previously on Political Calculations

We've been covering Arizona's experience with the coronavirus pandemic since the state first became a national hotspot early in the summer of 2020. Here's our previous Arizona coronavirus coverage presented in reverse chronological order, with a sampling of some of our other COVID analysis!


We've continued following Arizona's experience during the coronavirus pandemic because the state's Department of Health Services makes detailed, high quality time series data available, which makes it easy to apply the back calculation method to identify the timing and events that caused changes in the state's COVID-19 trends. This section links that that resource and many of the others we've found useful throughout the coronavirus pandemic.

Arizona Department of Health Services. COVID-19 Data Dashboard. [Online Application/Database].

Maricopa County Coronavirus Disease (COVID-19). COVID-19 Data Archive. Maricopa County Daily Data Reports. [PDF Document Directory, Daily Dashboard].

Stephen A. Lauer, Kyra H. Grantz, Qifang Bi, Forrest K. Jones, Qulu Zheng, Hannah R. Meredith, Andrew S. Azman, Nicholas G. Reich, Justin Lessler. The Incubation Period of Coronavirus Disease 2019 (COVID-19) From Publicly Reported Confirmed Cases: Estimation and Application. Annals of Internal Medicine, 5 May 2020. https://doi.org/10.7326/M20-0504.

U.S. Centers for Disease Control and Prevention. COVID-19 Pandemic Planning Scenarios. [PDF Document]. Updated 10 September 2020.

COVID Tracking Project. Most Recent Data. [Online Database]. Accessed 15 December 2020.

More or Less: Behind the Stats. Ethnic minority deaths, climate change and lockdown. Interview with Kit Yates discussing back calculation. BBC Radio 4. [Podcast: 8:18 to 14:07]. 29 April 2020.

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