Wednesday, May 20, 2020

Virtual Meetup

Back before the pandemic, we hosted meetups every month or two for people who read Slate Star Codex, the blog I spend a good deal of time on. People came over to our house on Saturday afternoon for food and conversation — typically twenty to forty people — starting at 2:00, ending at 10:00. I'm trying to revive the meetups online, using Mozilla Hubs. People who read this blog and don't read Slate Star Codex are welcome to come. Feel free to invite friends — from anywhere in the world.

Zoom and its competitors are designed for a one to many interaction, such as a lecture. Hubs is a VR program, usable from your browser or with a VR headset. It puts you in a world, in this case a house of four rooms that I have constructed online. The closer you are to someone, the louder his voice, so it is possible to have multiple conversations going and for an individual to wander around listening for an interesting one to join. That's how our meetups worked, and I am trying to construct the equivalent online.

For those interested in the general idea, there is another program also worth looking at — Online Town. Hubs gives you a virtual world rather like World of Warcraft, with your character moving around in it. Town is a top down view of a two dimensional world, with each person represented by a tiny icon. The nice thing about it is that when you get close enough to other people to talk with them you get to see their faces, a webcam view like what you get on Zoom. So you are having a conversation with people whose faces you can see, unlike Hubs, but there can be multiple such conversations going on at once and you can move among them, unlike Zoom. I may eventually try that as an alternative.

The link for the meetup, along with a link to information about Hubs, is a page on my site. It starts at noon, will presumably go until everyone leaves.

Sunday, May 03, 2020

How to Test a Vaccine

I have been making some calculations on the alternative ways of testing a vaccine, and unless I misunderstand something, the current procedure not only takes longer, it probably kills more people. Here are my calculations:

Method 1: Give the vaccine to N1 people. Wait a month. If none of them get the disease, conclude that the vaccine works. 

Method 2: Give the vaccine to N2 people. Deliberately expose all of them to the disease. If none of them get the disease, conclude that the vaccine works.

The following calculations assume:

A: We select N1 and N2 to reduce the chance of a false positive to no more than .05 .

B: Someone not already immune who is deliberately exposed has a .5 chance of catching the disease.

C: The probability that the vaccine works is .1, but if it works it works perfectly — probability of catching the disease zero.

D: The probability that the vaccine not only does not work but gives the recipient the disease is .01 .

In the U.S. at present, about one person in a thousand gets the disease each month, so with method 1, in the U.S., if the vaccine does not work each test subject has a .001 probability of getting the disease. So if it does not work, the probability that none of them get the disease is .999^N1. If we set N1=3000, that comes to about .05.

With method 2, if the vaccine does not work, the probability that nobody gets the disease is .5^N2. We set N2=5, giving us a probability of about .03.

With method 1, the expected number of people who get the disease because of the vaccination is .01xN1=30. The number who get it because because they are in the test and the vaccination doesn’t work is zero, since their exposure is the same as if they were not in the test. The number who avoid getting the disease as a result of being in the test and the vaccine working is .3 . Net increase in disease due to Method 1 is 29.7 .

With method 2, the expected number of people who get the disease because of the vaccination is .01xN2=.05. The number who get it because of the exposure (and the vaccine doesn’t work) is .9x.5xN2= 2.25 . The number who don’t get the disease as a result of being in the test and the vaccine working is .0005. So the net increase in disease due to Method 2 is 2.3.

For simplicity, I am calculating the number of people in the test who don’t get the disease as a result of the vaccine over a month in both cases. It’s small with Method 1, trivially small with Method 2. 

Adding all of this up, Method 1 results in 29.7 people getting the disease as a result of the vaccine trial, Method 2 results in 2.3 people getting the disease as a result of the vaccine trial. Method 2 also gives a somewhat lower chance of a false positive and produces a result about a month faster. 

This is obviously a simplified analysis — a vaccine doesn’t have to work perfectly to be worth using, and my particular numbers were invented. But given how much larger the first figure is than the second, the argument that we must use the first because the second is too dangerous looks implausible unless one believes that the chance the vaccine gives people the disease is lower than the chance that it prevents the disease by substantially more than an order of magnitude. 

Also, even if there is no chance that the vaccine causes the disease, the downside of Method 2 is tiny. A small number of people, two or three with my numbers, get the disease as a result of the test. Since you will be using healthy young adult volunteers, the chance of death for each is about one in a thousand. Getting a vaccine out a month sooner, on the other hand, saves about 20,000 lives in the U.S. alone. 

Am I missing anything? Is there any plausible set of assumptions under which Method 1 is better than Method 2? Alternatively, have I misunderstood what the methods are?