Monthly Archives: July 2009

The base rate fallacy

Amongst my favorite fallacies lies the base rate fallacy.

Here’s a great introduction to this fallacy on the BBC’s website.

Imagine you’ve invented a machine to detect terrorists. It’s good, about 90% accurate. You sit back with pride and think of the terrorists trembling.

You’re in the Houses of Parliament demonstrating the device to MPs when you receive urgent information from MI5 that a potential attacker is in the building. Security teams seal every exit and all 3,000 people inside are rounded up to be tested.

The first 30 pass. Then, dramatically, a man in a mac fails. Police pounce, guns point.

How sure are you that this person is a terrorist?
A. 90%
B. 10%
C. 0.3%

What is your brain lying to you about?

There are ways for your brain to lie to you, which pretty much guarantee you’ll never know it. Even if someone points out the exact way in which you’re being lied to, you probably won’t accept it. Even if a being that is proven to be smarter and more right than any human being who has ever lived tells you, the chances are good you won’t believe it.

As Yudkowsky says:

I find it disturbing that the brain has such a simple macro for absolute denial that it can be invoked as a side effect of paralysis. That a single whack on the brain can both disable a left-side motor function, and disable our ability to recognize or accept the disability. Other forms of brain damage also seem to both cause insanity and disallow recognition of that insanity – for example, when people insist that their friends have been replaced by exact duplicates after damage to face-recognizing areas.

The very idea is frightening.

These videos will make you smarter

Check out SixtySymbols. A collection of videos from smart people who explain the purpose and ideas behind different scientific symbols. Very interesting!

A random sample: