Last night PM Boris Johnson advised everyone over 70 to stay indoors for the next three months, while asking everyone else to "social distance." Today we adopted a rather liberal interpretation of what is required of us. Of course we both took long walks in Kensington Gardens and Hyde Park, which is well within the spirit of what has been asked. However, what Boris has asked is that we not sit down anywhere in public. This prohibits us from indulging our deeply-ingrained habit of going to a pub for lunch every day. In fact, we haven't eaten lunch together in our house for several years. (When Kathy has a lunch engagement with a friend, I go to a pub by myself. When I have a lunch engagement with a friend, she eats sushi at home.) One of our go-to pubs is the Duke of Clarence, a seven-minute walk from our house, on the Old Brompton Road. Except when there's an important rugby, football or cricket match on TV, there's hardly ever anyone in the Duke at lu...
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.
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 ...
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