Unexpectedly Intriguing!
11 March 2021

COVID-19 has continued its retreat in Arizona. Since our last looks at the state's high quality data, the numbers of new cases, hospital admissions, deaths, and ICU bed usage have each continued falling. There are signs however the rate at which they are falling is starting to slow.

That much can be seen in the following four charts, in which the back calculation method identifies the more significant events that have marked turning points during Arizona's experience in the coronavirus pandemic.

Arizona Positive COVID-19 Test Results by Date of Sample Collection, 1 January 2020 - 9 March 2021
Arizona New COVID-19 Hospitalizations by Date of Admission, 1 January 2020 - 9 March 2021
Arizona New COVID-19 Deaths by Date of Death Certificate, 1 January 2020 - 9 March 2021
Arizona COVID-19 ICU Bed Usage, 10 April 2020 - 9 March 2021

Since our last update, the success of the COVID-19 vaccination effort within the state has become more evident in the state's high quality data. With the large scale effort beginning in the last week of December 2020, its success can be seen in the more rapid declines that have occurred about two to three weeks later, coinciding with the period needed for the first dose of the vaccines to become effective.

Through 9 March 2021, roughly one in five Arizonas have received at least one dose of the available COVID-19 vaccines, and nearly 60% of the highly vulnerable Age 65+ population. The following two charts show the success of Arizona's COVID vaccine administration program. The first chart indicates the cumulative number of first and second COVID-19 vaccine doses administered in Arizona through 9 March 2021. The second chart shows the ratio of the portion of Age 65+ Arizona's reporting positive COVID-19 test results to the Age 0-19 population. This latter chart is significant for indicating the effectiveness of the COVID-19 vaccines because while nearly 60% of the Age 65+ population in the Arizona have been vaccinated, almost none of the state's Age 0 to 19 year olds have been.

Arizona: Reported Number of COVID-19 Vaccine First and Second Doses Administered, 1 December 2020 - 9 March 2021
Arizona Ratio of Age 65+ Population to Age 0-19 Population Reporting Positive COVID-19 Test Results, 1 October 2020 to 9 March 2021

Unlike its higher quality data, Arizona's age-demographic data for reported positive COVID-19 test results on any given date is 'contaminated' by test results that were performed on other dates. Although this issue makes the reported daily data less reliable than the state's higher quality data, it still generally follows same pattern, but is subject to noise. Such as happens whenever test labs in the state work to clear a backlog of test samples that accumulated over a period of several months.

Regardless, the age-ratio chart also confirms the success of the COVID-19 vaccines of the Age 65+ population when compared with the unvaccinated Age 0-19 control group in Arizona.

Previously on Political Calculations

Here is our previous coverage of Arizona's experience with the coronavirus pandemic, presented in reverse chronological order.


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: Vaccine Administration. [Online Database]. Accessed 10 March 2021.

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.

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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