Thomas Bayes and O.J. Simpson

After posting about The Prosecutor’s Fallacy I recalled a similar case with the Defense in the O.J. Simpson trial. The issue was summarized in What is your favorite problem for an introduction to probability?:

… one of Simpson’s lawyers, Alan Dershowitz, noted that even though Simpson beat
his wife, that hardly mattered, because in the United States, four million women are
battered every year by their male partners, yet only one in 2,500 is ultimately
murdered by her partner (1 in 1000), so, by the ‘reasonable doubt’ criterion, this is
irrelevant. The jury found that argument persuasive, but it’s spurious. The relevant
question was what percentage of all battered women who are murdered are killed by
their abusers, which ain’t 1 in 1000, but rather 9 in 10.

For a clear explanation of the details see Chances Are, by Steven Strogatz, which is reprinted in his excellent book, The Joy of x: A Guided Tour of Math, from One to Infinity.

The Language of Space

Want to be an Astronaut? Learn How to Speak Russian

You may wonder: “Shouldn’t Cosmonauts have to speak English?” I expect most of them learned it long before joining the space program.

In fact the situation is not symmetric. American astronauts as well as Russian Cosmonauts fly to space from a Russian-speaking site (the Baikonur Cosmodrome) in a Russian vehicle (the Soyuz).

The Prosecutor’s Fallacy

Bayes’ Theorem … A Simple Example

Notation: Prob(A) means “the probability of event A” and Prob(A|B) is “the probability of event A, given that event B has happened.”

Bayes’ Theorem: Prob(A|B)xProb(B) = Prob(B|A)xProb(A)

Now, Prob(A|B) and Prob(B|A) are often confused by even the most intelligent of people. The confusion often appears in legal cases and is sometimes called the Prosecutor’s Fallacy. Bayes’ Theorem relates these two distinct conditional probabilities.

Followed by a straightforward example of why this really matters.

Free the Quarks!

Calculating the strong force

A watershed: the emergence of QCD

We had arrived at a very specific candidate theory of the strong interaction, one based on precise, beautiful equations. And we had specific, quantitative proposals for testing it.

See also the Bag Model of Quark Confinement. Corry Lee gave a great explanation of this in her talk about the Higgs Boson at Chicon 7 last summer.