Unexpectedly Intriguing!
19 October 2021

We are seeing an unexpected development in Arizona's experience with the coronavirus pandemic. While the trends for the number of cases and deaths in the state are showing a slow, steady decline, the number of new hospital admissions in the state have plunged by a much larger amount by comparison.

The following chart shows the state's data for all three of these COVID-19 data series from 15 March 2020 through 15 October 2021, or rather, their rolling seven-day moving averages for which the data is at least 95% complete:

Arizona's Coronavirus Pandemic Experience, 15 March 2020 - 15 October 2021, Snapshot on 16 October 2021

According to the state's data, the number of new hospital admissions has fallen by over 57% from their third-wave peak during the week of 14 through 22 August 2021. That figure applies for 20 September 2021, which meets the 95% complete threshold at this writing. By contrast, Arizona had only seen a 23% decline in cases at the same point in time, which has grown to a nearly 33% reduction through 3 October 2021. The data for deaths through 20 September 2021 will be too incomplete to provide an additional point of comparison for another two weeks.

The Arizona Department of Health indicates their COVID dashboard is undergoing scheduled database maintenance, so this is the most current information available for the state until it might update it later today. We're curious to see if the state's data for COVID hospital admissions might be subject to revision when that work is complete.

If the hospital admission data is unchanged or only sees minor revisions, it suggests Arizona's experience with the coronavirus pandemic as its third wave recedes is very different from what it saw during its first two waves.

But if there's been a reporting glitch for new COVID admissions from Arizona's hospitals to Arizona's DHS, we would expect the states datatrend for COVID hospitalizations to follow the same basic pattern for as for cases. We'll update the original article on our site with what we find after the state's next COVID data update.

Update 19 October 2021, 11:15 PM EDT: The patterns we've described above have held through the latest daily update, which covers available data through 18 October 2021.

Previously on Political Calculations

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


Political Calculations has been following Arizona's experience with the coronavirus experience from almost the beginning, because the state makes its high quality data publicly available. Specifically, the state's Departent of Health Services reports the number of cases by date of test sample collection, the number of hospitalizations by date of hospital admission, and the number of deaths by date recorded on death certificates.

This data, combined with what we know of the typical time it takes to progress to each of these milestones, makes it possible to track the state's daily rate of incidence of initial exposure to the variants of the SARS-CoV-2 coronavirus using back calculation methods. Links to that data and information about how the back calculation method works are presented below:

Arizona Department of Health Services. COVID-19 Data Dashboard: Vaccine Administration. [Online Database]. Accessed 16 October 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]. 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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