Mathematics

Fauci is a great virologist, but he doesn’t seem to (automatically) do a back of envelope calculation before throwing out a statement. And so one of his most recent statements (on voting), doesn’t pass the smell test. So what happened? Fauci said this week there is “no reason” Americans can’t vote in person for the … Read more

It’s hard to present data in an insightful way. I always recommend that people check out the works of the statistician (and artist!) Edward Tufte (https://www.edwardtufte.com/tufte/) to learn more about how to do it. Graphs can be especially problematic because of how easily they can be used to mislead – even with no intention of … Read more

Whenever you look at a graph there is a tendency to see trends. Then you extrapolate into the future by extending the curve. To a mathematician this practice is extremely suspect. For example look at the following curve: What is going to happen next? Well your guess is as good as mine! But as a … 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

In a previous blog I said that we say that a test is very sensitive if it has very few false negatives. I then said that if all you know about the test is that it is a very sensitive test, only it’s negative results are truly informative! Getting a positive result i.e. you are … Read more

We know testing is all important to get through this. People need to know if they have active virus so they can adjust their behavior accordingly. Anyone who tests positive should self quarantine for 14 days and we also need to do contact tracing to find the people that they have been near to. (I … Read more