Archiver > GENEALOGY-DNA > 2010-11 > 1290278277

From: Steven Bird <>
Subject: [DNA] P value (was chances are, it's wrong)
Date: Sat, 20 Nov 2010 12:37:57 -0600
References: <F9C440A2-FC59-4A9E-AAAC-85DEE9D2FAB0@GMAIL.COM>, ,<COL115-W50D879F102DC3996D9D454A03A0@phx.gbl>, ,<>, ,<COL115-W1464B78AF0292D6AEFA183A03B0@phx.gbl>,<COL115-W5950BB2C58A31B4806036EA03B0@phx.gbl>,<>,<COL115-W45724B549DCDA5DD2EC4A0A03B0@phx.gbl>
In-Reply-To: <COL115-W45724B549DCDA5DD2EC4A0A03B0@phx.gbl>

James wrote:

> P-value has a very precise meaning in Frequentist statistics.
> It is "the probability of obtaining a test statistic at least as extreme
> as the one that was actually observed, assuming that the null hypothesis
> is true".

I reply:

It is also defined as the probability of committing a Type I error (rejecting the null when it is in fact true or a false positive) when using a statistic such as student's T test. When p=0.05, it means that the statistician have a 1 in 20 chance of being wrong (falsely rejecting the null) when the null is in fact true. To me, that is identical in meaning with the statement that he or she also has a 19 out of 20 chance of being right. How is it different?

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