Archive for September 16th, 2020

“Confirmed cases” skyrocketed … how many were false positives?

September 16, 2020

One answer to why there wasn’t a commensurate high spike in deaths.
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COVID tests yielding “false positive” results have been hitting the news again.

A couple of weeks ago, Ohio governor Mike DeWine tested positive, missed an event with President Trump and was subsequently re-tested (twice) and found to be negative.

See Ohio Gov. DeWine tests negative … after testing positive.

This week, it was reported that several nursing homes have experienced numerous cases of false positives.

False-positive test results are a particularly significant risk in nursing homes, because a resident wrongly believed to have Covid-19 could be placed in an area dedicated to infected patients, potentially exposing an uninfected person to the coronavirus.

And, there is a growing number of reports that re-opened schools are being shut-down when a single student or faculty member tested positive.  Locally, I know of 3 such instances.

Bottom line: false positives are very likely and have significant consequences to patients and institutions.

The IHME estimates that less than 1% of Americans are currently infected.

Given the low prevalence of COVID (i.e. percentage currently infected) … and low but statistically significant testing errors … the likelihood of false positives is very high!

Here’s my logic…

In my strategic business analytics course, I used to teach something called Bayesian Inference … a way to calculate probabilities by combining contextual information (called “base rates” or “priors”) with case-specific observations (think: testing or witnessing).

Today, we’ll apply Bayesian Inference to the COVID testing situation…

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Sept. 16: Election Odds & Polls

September 16, 2020

Biden +4.4 in odds, +6.8 in polls
Mideast peace agreements signed
Bloomberg: $100 million for Biden

RCP – Betting Average  of 6 books’ odds
Biden 51.6  Trump 47.2  Lead +4.4 

Trump Best:   49.7  49.8   + .1   Sept. 2
Biden Best :
   60.9  30.6  +24.3  July 23

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Predict It   online betting site
Biden 58  Trump 45  Lead 13

Trump Best Aug 31:   53 48 +7
Biden Best July 23
 :   63 39 +24

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RCP – Poll of Polls
Biden 49.7  Trump 42.9  Lead 6.8
Undecided 7.7
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538 – Chance of Winning  Nate Silver
Biden 76  Trump 24  Lead 52 

Sept. 16: C-19 Data Dashboard

September 16, 2020

200,171 Deaths-to-Date

1,171 Daily New Deaths  (peak 2,824 April 21)
> 7-day average 884       (peak 2.229 April 23)

35,925  New Cases
> 7-day average  36,058

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Details below…

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