Learning how to do “back of envelope” calculations is one of the most important tools you can master – it is a damn shame we don’t spend more time on them in school. The idea is you make some assumptions, round up and down often, so you can get a rough idea of what a … Read more
Sometimes the mathematician in me want to tear my hair out when I listen to the news. A 50% effective vaccine won’t stop the Pandemic, better drugs won’t stop the pandemic, the only thing that can stop the pandemic in both the short and long run is to bring the effective transmission rate r t … Read more
One of the great unsung heroes in my lifetime was a polymath named Frances Oldham Kelsey who, in an era when women had to overcome so much, earned both a PhD in pharmacology(1938) and an M.D.(1950). In 1960 she became “one of just a handful of medical officers” at the FDA. “One of the first … Read more
Well, you can do that if you keep in mind that there are three key numbers: The test positivity rate The total number of positive test recorded Number of new hospitalizations And, you also keep in mind that what is important is not only the numbers themselves but also if the numbers are increasing, staying … Read more
A short post but an important one. I’ve said it before and I’ll say it again because it can’t be repeated enough: if you are told the increase in testing is why there is a rise in confirmed cases, check the test positivity ratio. If it is the same (or even worse, increasing), then the … Read more
Every day when I watch the news they show graphs of which states have an increasing number of cases. Guess what? That information doesn’t tell you much if anything at all. They are to be blunt essentially useless graphs and innumeracy writ large. It makes me angry and to paraphrase a friend: “when I get … Read more
I promised you the answer to the calculation that the Harvard medical school people got so terribly wrong, but because of some news I saw in the NY Times today (https://www.nytimes.com/2020/06/01/health/masks-surgical-N95-coronavirus.html), I wanted to do a quick post updating my post: garycornell.com/2020/04/21/multiplication-of-probabilities-or-what-to-do-when-you-have-to-go-shopping In that post, I first guessed about what the various probabilities might be … Read more
I promised in my last blog to show you how to do the calculations of whether or not you really have that disease when you tested positive. The calculations aren’t hard but they are always a bit tricky. So fair warning, if you really want to understand how to do the calculations, you should really … Read more
Let’s suppose you have an exquisitely accurate test. Hey it even meets the gold standard: it’s 99% specific and 99% sensitive. Tests don’t get much better than this. Recall that being 99% specific means you are only going to get one false positive when you test 100 people who do not have the disease and … Read more
Recall that a test’s sensitivity is the percentage of false negatives you get. If you test 100 people known to have the disease and your test says 99 of them have the disease that is a 99% sensitive test. Or, in other words, you take the number of really positive people your test found (99) … Read more