Revisiting the Estimation of Unconfirmed Cases of COVID-19 in Whatcom County

[Co-author of this article is Ronald E. Cossman, Ph.D., a Research Professor and Research Fellow at the Social Science Research Center at Mississippi State University. He also directs the Mississippi Center for Healthcare Workforce. His work focuses on the intersection of socioeconomic factors, geography and health in Mississippi, the South and the nation. His work has been funded by NIH, HHS, EPA, the Annie E. Casey Foundation and the Mississippi Department of Health. His PhD is in geography from the University of Colorado, Boulder, and his Masters is in Demography and Population Studies from Florida State University.]

In an NWC story that appeared on April 14th and used a total confirmed Covid-19 case count of 263, we described a method and data that we used to arrive at an estimated 1,973 people in Whatcom County who were unconfirmed, but COVID-19 positive. Using this as point of departure, we then refined the method, wrote it up in an academic paper and submitted the paper to a public health journal, where it is still under review.

Employing the refined method, we compare our estimate of unconfirmed Covid-19 cases as April 24th to an estimate based on a statement made on June 24th by Dr. Robert Redfield, the Director of the Centers for Disease Control and Prevention, that evidence suggests there are ten times more cases than reported. Unlike many statements coming out from the current administration, this one was based on science. In this case, serology tests. As such, it is believed at this point that the “ten-fold” multiplier yields an accurate estimate of unconfirmed cases, a “gold-standard,” if you will for this point in time.

As of April 24th, there were 284 total reported cases and 257 reported active cases for Whatcom County. So, using the ten-fold multiplier, we would have expected 2,840 total cases and 2,570 active cases in Whatcom County, Washington as of April 24th. In our academic paper, available at Researchgate as a “preprint” under the “Publications” section, we estimated that there were 2,670 total cases unconfirmed cases with a 95% confidence interval from 2,025 to 3,936. As you can see, the 2,840 number falls well within the 95% confidence interval and is only 6.37 percent higher than our estimate. In terms of active cases, the ten-fold multiplier yields an estimate of 2,570 “active” cases as of April 24th for Whatcom County, Washington, which is well within the 95% confidence interval, 1,832 to 3,559 and, as found earlier for total cases, only 6.37 percent higher than our estimate of 2,416.

The less-refined method we described in the NWC article of April 14th is reasonable, but not as accurate as the more refined one. It basically multiplies the number of reported cases by 7.5. Using this multiplier with the 284 total confirmed cases reported for April 24th yields an estimated 2,130 unconfirmed total cases. The ten-fold estimate of 2,840 is 33 percent higher as would be the case if we applied this multiplier to the number of active cases.

Our academic paper benefited from informal peer reviews before we submitted it to a peer-reviewed journal. The fact that the method we describe in it provides estimates quite close to that expected under the current “gold standard” is a testament to the value of the norms used in scientific studies, particularly, objective peer reviews. Accordingly, as time goes by and new evidence emerges, these estimates will surely themselves become more refined, a testament to the value of the scientific method.

About David A. Swanson

Posting Citizen Journalist • Member since Mar 31, 2020

David A. Swanson is Edward A. Dickson Emeritus Professor of Sociology, University of California Riverside. He served as a member of the U. S. Census Bureau’s Scientific Advisory Committee [...]