Archiver > GENEALOGY-DNA > 2010-11 > 1290209791

From: Steven Bird <>
Subject: Re: [DNA] Odds Are, It's Wrong - 5% of the time
Date: Fri, 19 Nov 2010 17:36:31 -0600
References: <F9C440A2-FC59-4A9E-AAAC-85DEE9D2FAB0@GMAIL.COM>
In-Reply-To: <F9C440A2-FC59-4A9E-AAAC-85DEE9D2FAB0@GMAIL.COM>

The headline should have read:

"Tom Sigfried fails to display any real understanding of statistics."

95% confidence interval means that you have a 1 in 20 chance of being wrong. If that isn't good enough for your purposes, then use a broader confidence interval, say 99.7% (3 sigmas). There's no mystery here.

A steroids test that misidentifies 5% of the time is a bad test. Don't use it. However, if I have a 19 out of 20 chance of winning a bet, I'll take it. If I lose, I'll do it again double or nothing. Then the odds are now .05 *.05 that I will lose, or .0025. Third times a charm! Double or nothing at .05*.05*.05=.000125, or .0125% chance I'm wrong; about one chance in a thousand that I will lose three times in a row. I'll take those odds any time.

Now, if I had a only 95% chance of making it home in my car tonight (5% chance of a fatal accident) I would probably consider postponing the trip to a more favorable time. :-) It all depends on your needs.

> Odds Are, It's Wrong: Science fails to face the shortcomings of statistics
> By Tom Siegfried
> Science News, March 27th, 2010; Vol.177 #7

This thread: