Using Shewhart Charts to Understand Variation in COVID-19 Reported Deaths
IHI and our colleagues have developed a COVID-19 Data Tracker application showing the reported deaths from COVID-19 globally using Shewhart charts.
Shewhart charts, a cornerstone of improvement methods, are designed to distinguish between common cause (random) and special cause (non-random) variation, they are ideally suited to help decision makers understand if the reported number of daily deaths is predictable within limits or unpredictable (i.e., special cause variation).
The IHI COVID-19 Data Tracker has Shewhart charts for: 1) individual countries and 2) US states and territories.
Shewhart charts are updated daily for each country and each US state and territory. The model tracking the trajectory of COVID-19 reported deaths detects when the number of deaths by geographic location is entering rapid exponential growth (Epoch 2) and when exponential growth has ended. We believe that the Shewhart chart approach will prove to be useful to subject matter experts, decision makers, care providers, and the public as they address COVID-19 challenges.
- View the
detailed instructions for the COVID-19 Data Tracker to learn how the Data Tracker is organized, key terms used to display the data, and guidance on how to navigate the various screens.
- It is important to understand the
key terms used to create and interpret the Shewhart charts:
- Epochs: Pre-Exponential Growth (Epoch 1); Exponential Growth (Epoch 2); Post-Exponential Growth with flat trajectory or exponential decline (Epoch 3); Stability after descent (Epoch 4)
- Extensions: When a phase is “active” the upper and lower control limits and center line are extended as reference markers for 10 days
- Adjusted versus Unadjusted Data: The raw data (unadjusted) reflect the number of deaths submitted by numerous sources tracking COVID-19 deaths, which include “spikes” or extreme data points that do not typify the general historical patterns in the reported data; the Adjusted data attempt to create a more stable stream of data from the various data sources
- Ghosting unusually large data values: Each daily record is examined to assess if the record is unusually large compared to days preceding and following the record; on the Shewhart charts these unusually large data points are referred to as being “ghosted”
- Use the
Full Screen mode (click arrow icon, bottom right) to see the charts in a full browser window.
Charts for Individual Countries: COVID-19 Reported Deaths by Country
Select Country: On the far left, click the circle to the left of the country name. (Use Full Screen mode to view larger.)
- Countries are listed in alphabetical order on the left side. Note that the screen opens with the United States as a default.
- The data shown on the chart are Adjusted Data. To view the chart with Unadjusted Data, click on the box in the lower left corner labeled “Click for Unadjusted Daily Deaths.”
- You can also view the Unadjusted number of reported deaths by clicking on the “2” in the label at the bottom center of the chart that looks like this: <1 of 2>
- To view a specific date range on a chart, use the “slider” (located along the bottom of the chart) to select the date range you wish to review.
Download detailed instructions
Charts for United States: COVID-19 Reported Deaths by US State and Territory
Scroll Through Pages: Use the left/right arrows in the gray area at the bottom to scroll through pages: Summary chart, Adjusted Deaths charts, Unadjusted Deaths charts, and Credits. (Use Full Screen mode to view larger.)
- The charts for the US States and Territories follow a similar layout as outlined above for the Individual Countries, but there are a few additional options.
- Summary: The US Summary chart provides a “system view” of the states and territories that are in each Epoch over time.
- State/Territory Adjusted and State/Territory Unadjusted: Selecting either option automatically activates a chart showing the states and territories in Epoch 1; you can select a specific state's data to review from this screen, and you can also select which Epoch to view.
- “What Are Epochs?” (in the lower left corner): Definitions of the four Epochs
- Use the “slider” to revise the dates along the horizontal axis and zoom in on a particular time period.
- Use the forward (>) or back (<) arrows to switch between the Summary chart (Page 1), Adjusted Deaths charts (Page 2), Unadjusted Deaths charts (Page 3), and Credits (Page 4).
Download detailed instructions
The IHI Data Tracker uses COVID-19 data from the
New York Times GitHub site for the US states and territories charts and the
Our World in Data site for the country-specific data.
- Read a more
detailed explanation of the methodology behind the Shewhart charts used in this application on the New York Times GitHub site.
- Read an article that provides a description of initial development of the Shewhart chart application:
Understanding variation in reported COVID-19 deaths with a novel Shewhart chart application [Perla RJ, Provost SM, Parry GJ, Little K, Provost LP. International Journal for Quality in Health Care. 2021;33(1).]
- Watch the
Science of Improvement Whiteboard videos on the IHI website which describe Shewhart charts and their use.
- For those interested in the details behind Shewhart chart construction and use:
The Health Data Guide (Provost L, Murray S. Jossey-Bass Publishers; 2011)
Quality Health Care: A Guide to Developing and Using Indicators, 2nd Edition (Lloyd R. Jones & Bartlett Learning; 2019)
IHI COVID-19 Data Tracker Team
Lloyd Provost, Principal Statistician, Associates in Process Improvement
Shannon Provost, Lecturer, The University of Texas at Austin
Rocco Perla, Co-Founder, The Health Initiative
Kevin Little, Improvement Advisor, Informing Ecological Design, LLC
Neel Vora, Vice President, Information Technology, Institute for Healthcare Improvement
Robert Lloyd, Vice President Improvement Science and Senior Improvement Advisor, Institute for Healthcare Improvement
For inquiries about navigating and using the IHI COVID-19 Data Tracker, email Robert Lloyd (firstname.lastname@example.org).
How to Cite This Content: COVID-19 Data Tracker: Using Shewhart Charts to Understand Variation in COVID-19 Reported Deaths. Boston: Institute for Healthcare Improvement; 2021. (Available on
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