January 4th, 2004

breaking bad


I've got a bad cold, and I was half-awake most of the night. Bah. I don't enjoy maths but sometimes when I've got a temperature I find maths running through my head. It was arising from the post I made a couple of days ago about the gender genie. I'm going to post it just to get it out of my system.

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I think this statistical 'trick' is very important to understand, because a lot of the data we read every day, from forensics, medicine, economics, and of course the paranormal, are results of this kind. And it is kind of counter-intuitive. You imagine that the success rate of a test indicates how good the test is. But it doesn't. Not unless you control the sample composition. And to control the sample composition you need a reliable test. It's Catch 22.

Instead you have to go back to the raw data, and usually that is not possible. This is why I am so suspicious of official statistics.