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Archiver > GENEALOGY-DNA > 2010-11 > 1290260103


From: Steven Bird <>
Subject: [DNA] FW: Odds Are, It's Wrong - 5% of the time
Date: Sat, 20 Nov 2010 07:35:03 -0600
References: <F9C440A2-FC59-4A9E-AAAC-85DEE9D2FAB0@GMAIL.COM>,<COL115-W50D879F102DC3996D9D454A03A0@phx.gbl>,<4CE7A3C0.7050702@ucl.ac.uk>,<COL115-W1464B78AF0292D6AEFA183A03B0@phx.gbl>
In-Reply-To: <COL115-W1464B78AF0292D6AEFA183A03B0@phx.gbl>


James wrote:


>
> No. A 95% confidence interval does NOT mean that you have a 1 in 20
> chance of being wrong.
>
> Unfortunately, the fact that confidence intervals are still so
> misunderstood (as witnessed by your post; and also people still using
> confidence methods rather than Bayesian methods to report eg ranges of
> plausible TMRCAs) shows that, sadly, there still remains a need for
> articles like this even 80 years on.
>

The Frequentist definition of a p value of 0.05 is that the person conducting the t-test (or whatever test is being used) has a one in twenty chance of being wrong, simply due to bad luck. That means that 19 out of 20 times, on average, the experimenter is right. If that is not good enough, you only accept a lower p value before rejecting the null.

I realize that a CI of 95% is not identical to a p=0.05; sorry for conflating the terms.

What Bayesian statistics does is another matter altogether and is therefore called a "credible interval."














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