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The base rate fallacy

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As testing for Covid-19 immunity becomes widely available, it's important to understand the "Base Rate Fallacy" that leads people who test positive to reach false conclusions about the true probability that they are actually immune.  Let's assume that 10% of the population is immune. Epidemiologists refer to this as the population's "base rate" of immunity. If the base rate is 10%, there's a 10% chance that a randomly-selected individual is immune.  Now test that individual for immunity with a test known from clinical trials to result in 5% false positives. this means that 5% of the time, individuals testing immune actually are not. Let's also assume that the test doesn't result in any false negatives, meaning that everyone who is immune will test immune.  When we use this test on our randomly selected individual and she tests positive (immune), what is now the probability that she really is immune? The answer is that a positive test changes

To Furlough or to Unemploy?

One of the lessons that USA should learn from Wave One and follow in planning for Wave Two is that it is better to furlough than to unemploy. In many European countries, government policy during Wave One has been to advise business to furlough workers rather than unemploy them. Furloughed workers keep their jobs, and continue receiving their salaries. Businesses who furlough their employees are reimbursed by government for the full cost of their workers salaries. USA's Wave One policy, by contrast, is a combination of unemployment insurance and the Payroll Protection Plan. If the USG had thought it through before Wave One happened, it would have realized that relying on the traditional system of paying benefits to unemployed workers would be a mistake, because that system is designed for workers who lose a job they don't expect to return to. Unemployment benefits sare meant to tide unemployed people over while they look for new job.   The furlough approach recognizes that the v

The chronology

Since the election will largely be conducted as a blame game, chronology will be important. Here are two accounts from NYT and the  Washington Post

Vaccine by September?

The Times of London reports today that a vaccine may be ready by September.  And Bill Gates says his foundation is going to spend billions to manufacture many different vaccines, knowing that most of them won't work, in order to speed the process of finding one that does. 

Trump versus science

Trump believes that the scientific community is vulnerable to a kind of herd immunity. Scientists immunize themselves against the career-limiting consequences of being wrong by following the herd.  From this it follows that the concensus of the scientific community is always suspect, and never more reliable than the view of an informed (or uniformed) outsider who has had no enagement with the facts and reasoning of the scientific community.

Day Seventeen

In the UK, as elsewhere, we are grappling with balancing death by coronavirus versus death (economic and physical) by deprivation, we are hearing a renewed call for relaxing the restrictions and allowing the virus to do what it will. Here's the logic.  So long as we ward off the spread of the virus by locking down, we only delay the inevitable, which is that everyone will eventually be exposed. Wherever restrictions have been relaxed after new cases have dropped off, new cases have rebounded. This includes Wuhan and Hubei province. So we can prevent the second wave indefinitely by remaining locked down indefinitely, and collapsing the economy indefinitely. Or we can relax the restrictions, and revive the economy to the degree that we do, and release the virus to infect more people to the degree that we do.  Indefinite cratering of the economy, and everything that comes with that, cannot be an option. So let us out to die, if that is our fate. Hydroxychloroquine is Trump&

Day Two

There has been some strenuous kick-back from my daughters, mainly Lily, and to some extent my wife, against my liberal definition of "isolation" to include sitting down in a coffee shoppe or a pubbe. I will not attempt to justify my approach to this question -- for example, by pointing out that I routinely use "99.9% effective" anti-bacterial wipes to disinfect all metal, glass and plastic surface I come into contact when I sit down, and that I never sit within 20 feet of another human being, which is not hard to do given how few people are now out and about. Instead, I will bow to public pressure. Henceforth, until further notice, I will not sit down in any public place. However, I reserve the right to issue further notice at a time and place of my own choosing.