Part 2 – Manipulating Positivity and Reported Deaths
The Trump campaign spews misinformation, trying to convince the electorate that the administration’s response to Corona-19 has been effective. In Part 1, we focused on how (mostly) Republican governors are limiting testing in order to reduce “Confirmed Cases” (Please read first, if you haven’t already).
In that post, we introduced this equation:
(a) [Confirmed Cases] = [People Tested] x [% positive]
Using Florida as a case study, we focused on how the state has reduced its Confirmed Case Count by cutting back dramatically on the number of [People Tested], at a time when best-practice suggests increased testing is warranted.
In this post, we’ll focus on the second variable, [% positive], aka “positivity”, and how it is being manipulated to obscure the reporting of the pandemic, including official reporting of death counts. As we’ll see, these manipulations are creating the appearance of progress against the Pandemic in the run up to the election, but masking the true impact of the disease, and potentially risking thousands of additional deaths.
Why Test at All? A Scenario
There are many reasons for testing, but the most common (and important) is to identify people who are infectious, to isolate themselves, and thereby breaking the cycle of contagion.
Consider this scenario:
Your best friend calls you to say that he’s been diagnosed with COVID. Six days earlier, you hosted him for dinner at your home. Your friend started to feel sick the day after the dinner, procrastinated a day thinking it was allergies, then got tested. Three days later, today, he gets a positive result and he’s called you immediately to give you the bad news.
You’d been reasonably responsible during the dinner party, which was mostly outdoors (though it was a still evening with no wind). He’d spent half an hour conversing with you in the kitchen as you prepared the meats for the BBQ, not always masked, everyone had used the same downstairs powder room, and while you ate outdoors, you drank wine, and talked until the small hours, only a few feet apart.
Should you get tested? I certainly would want to, even if I felt no symptoms, and I suspect most folks would agree, particularly if you’re in a high-risk category (as I am due to age).
So, you go to the testing center and 48 hours later get the good news, negative. However, a few days later you start coughing. So, you get tested again and the result this time is positive.
How does this get reported? According to CDC guidelines, the two tests would both be recorded on the case reporting form, but in the testing summary reports, you’d be listed as a single person tested, with a single positive result. Your personal “positivity” would be 100%.
As you recover, you get additional tests to help determine if you’re still communicable. After 10 days you’re still testing positive, but that result would not change your positivity score. Nor, after another week, when you test negative, does that undo your earlier positive score. It all gets grouped within your case file (and a reason why a Confirmed Case is a thing).
It makes sense.
Most states report positivity following these guidelines. But, Florida mostly does not.
You can figure out the conventional positivity number if you dig into the DOH County Report and calculate it yourself. You can also download the Covid Tracking Project’s reporting, which aggregates the same numbers to the state level. This allows you to compare Florida to other states.
Calculated the CDC-recommended way, Florida’s positivity was 13.9% for the week ending 8/23. This is an important number for several reasons, but specifically, positivity above 10% is considered a dangerous level, and a sign that more testing is needed.
However, if you go onto the DOH’s COVID-19 Data and Surveillance Dashboard, it will tell you that the positivity for the same week ending 8/23 was 5.83%. Huh?
Turns out that Florida does its own, non-standard, and widely-criticized positivity calculation. Essentially, the state counts only a single positive result but, contrary to CDC guidelines, counts all of the individual negative results. These controversial measures also appear on the County Report as the so called “New” Test/Pos/Neg. If you calculate the way the State of Florida does on its dashboard, for the scenario we just discussed, your personal positivity would be 33% not 100%:
- The initial negative result
- The one positive result (but not the second)
- The final negative result
I can see no reason to do this other than to confuse the public, and allow Florida officials to claim a lower-sounding positivity rate. Most folks won’t understand the difference, so that if the state says “positivity” is less than 6%, and many other Sun Belt states are struggling with 10%+, Florida must be doing better, right? The fact that the Trump administration won’t enforce CDC reporting guidelines is another example of how the Administration is placing politics above the national interest.
We saw in Part 1 that Florida was cutting back on total testing numbers in order to reduce the number of confirmed cases. Given the continuing high positivity number (as the CDC would calculate it), you can be sure that there are many people who would like to be tested who aren’t. The question is, are the scarce tests being allocated fairly among the people who need them? Spoiler answer, no.
Allocating Testing in a Time of Scarcity
So how should tests be allocated? Absent scarcity or pricing barriers (i.e. if testing were free), you’d expect test demand to correlate strongly with the number of sick people.
So, an optimal scheme for allocating tests to counties would take into account both the base population of the county, and the positivity rate, in order to allocate more tests to the places where they’re needed.
Florida, instead, appears to allocate testing capacity solely by population. This has the advantage of being bureaucratically defensible, and fairly straight-forward, but leads to some less than optimal results.
As shown in Table 1, for the week ending July 17, counties with above-average positivity tested only 5% more than counties with below-average positivity. For the week of August 27, it was even worse, where the counties with higher than average positivity only managed 3% more testing.
Table 2 breaks this down for counties with the highest and lowest Positivity rates for 8/27. Column 5 of this table provides a Positivity Ratio of the 8/27 and 7/17 percentages. A ratio >1.0 means that positivity increased, <1.0, that it dropped. As a state-wide average, Florida’s Positivity dropped to 12.45% on August 27 from 17.89% on July 17, a 0.7 ratio.
Despite the drop state-wide, 18 of the 20 highest-ratio counties on 8/27 had experienced a Positivity increase. By contrast, 10 out of 10 of the lowest Positivity experienced a decrease at the state-average-rate or better.
In terms of testing rates, counties with Positivity Ranks 11-20 were particularly badly served by the state’s allocation methods, achieving only 589 tests/100k during the week. Equally unfair, the 10 counties at the bottom of the Positivity Ranking were able to test the most at 871/100k, 19.4% higher than the state-average testing level of 729/100k, and 47.9% higher than Counties 11-20 could achieve. This is far from optimal.
Why does the state allocate tests so inflexibly? I’m speculating. But realize that if the state were to allocate extra tests to high-positivity counties it would translate to a higher Confirmed Case count.
Impact on CFR
The Trump administration puts a big emphasis on the Case Fatality Rate, i.e. the percentage of Confirmed Cases who eventually died from COVID.
We did a deep dive on CFR a couple of weeks ago (Is FL 5x better than NJ?) which I don’t want to repeat here but is well worth reading. However, it’s worth noting a few key points:
- By reducing Confirmed Cases, the State of Florida is also reducing Confirmed Deaths
- Florida doesn’t follow CDC guidelines and does NOT report Probable COVID deaths as part of its official total. So, this misinformation is lowering the official death count substantially.
- Florida has been slowing-down death reporting. This improves apparent CFR even more than I estimated a couple of weeks ago. See, How a change in reporting policy created a dramatic chance in counting deaths.
This means that many Florida COVID deaths won’t be reported explicitly, and will only be understood over time, as excess deaths are identified and analyzed. This is slow process, especially if death reporting is trickling in. It will always be subject to gas-lighting and denial by the political powers that be.
In mid-August, I estimated probable COVID Deaths for Florida as an additional 47% on top of Confirmed Deaths. This was based on the CDC’s excess death estimates in July and early August, based mostly on Confirmed Cases created during a time when Florida was NOT purposefully cutting back on testing. Based on this current testing and reporting practices, excess deaths are likely to increase markedly. Keep in mind, however, it won’t be clear until mid-October at the earliest, given the long lag time between infection and death, particularly for the younger patients that Florida is infecting.
The State of Florida needs only keep-up this fiction, that the situation is improving, viable through the election. I hope this article will encourage more folks to dig deeper and expose what’s really going on.