Friday, August 17, 2012

Worshipping numbers

Some people worship numbers. Paradoxically, number-worshippers are bad with numbers. Because they are so bad with them, they’re unable to critically evaluate claims that involve numbers. You can make them believe almost any idiocy, as long as you use lots of made-up or otherwise incorrect numbers in the course of selling it to them.

Some time ago in the UK there was a criminal trial in which the defendant was a mother accused of killing her two babies. Her defense was that both her babies died of the sudden infant death syndrome. Prosecution called an expert witness, a pediatrician, who testified that, since studies show that the risk of a sudden infant death syndrome occurring in a family similar to the defendant’s is 1 in 8,500, the likelihood of two such deaths occurring in one family is 1 in 73 million. Because the prosecution, the jury, the judge, and the defense were all number-worshippers, this idiotic claim went completely unchallenged. He’s talking numbers. He must be right.

The defendant’s conviction was later overturned on appeal in which it was shown that the expert’s probability claim was completely bogus. Statisticians and health researchers have shown that, first, the assumption of independence is totally unwarranted, and second, that the original calculation involved unconditional probabilities where conditional probabilities should have been used instead. But there is a far simpler reason why this calculation is ridiculous. In order to see this reason, you don’t even have to be good with numbers or know much about probabilities. All you need is a mind that thinks and does not worship numbers. One of the journalists reporting the initial trial saw it right away. Wait a minute, he said, are you telling me that the probability that this woman is innocent is 1 in 73 million? Surely this can’t be right. A great majority of mothers whose babies die did not murder them. But when, instead of thinking, you worship numbers, such simple truths are inaccessible to you. So you can wield your sanctimonious judgment on innocent people with a clear conscience.

(In this video you can learn about the details of the trial.)

Sunday, August 12, 2012

Soft drinks and GDP

I just read that Coca Cola in Poland employs about 2,700 people and produces 0.002 of Poland's GDP. If this is true, then assuming every worker had productivity on that level, Poland's GDP could be produced by a labor force of about 1.4 million people. (In reality it is almost 18 million people.) Or, equivalently, keeping size of labor force at current level but increasing everyone's productivity to Coke level, Poland's GDP per capita would be well over $100,000.

Saturday, August 11, 2012

My dear Mr. Babbage

I am very much obliged to you for sending me cards for your parties, but I am afraid of accepting them, for I should meet some people there, to whom I have sworn by all the saints in Heaven, I never go out.
(Charles Darwin to Charles Babbage.)

Friday, August 10, 2012

The customer is always right. But which customer?

How many times have you heard statements to the effect that bond credit ratings must be biased since institutions that issue bonds pay for these ratings? A lot, probably. These statements are shallow, and wrong. The fact that someone pays to be evaluated does not mean that the evaluation must be biased. If you decide to go to grad school, you'll probably have to take the GRE or some other standardized test. For that test, you'll have to pay the testing company. Does this mean your score will be biased in your favor? Definitely not. Why not? Because test scores, as long as they're not biased, provide schools with valuable information about prospective students, so they want those prospective students to be screened that way. If test scores were biased, schools would no longer require them, which means prospective students would not be willing to pay for them anymore. Even though test-takers pay to be tested, testing companies have strong financial incentives to keep test scores as honest as possible.

Tuesday, August 7, 2012

The most important Master's thesis of all time

Has been defended in 1936 by Claude Shannon, and is titled A Symbolic Analysis of Relay and Switching Circuits. In it, Shannon shows that certain electric circuits are isomorphic to Boolean algebra.