What is a P value? Does anyone can give a simple explanation? I am not using

an easy explanation with my students and maybe some of you are developing

something interesting during classes !

For example, comparing the mean weight of male (M) and female (F) fishes we

have: Mean of M = 2,46kg (n = 59) and Mean of F = 2,51kg (n = 59). Using a t

test, the result is: df = 116, t = 0,26 and P = 0,79.

Searching in books I have found different definitions. The explanation for P

= 0,79 could be.....

1 - the probability of Type I error.

2 - the probability of rejecting a correct null hypothesis.

3 - the probability of incorrectly rejecting the null hypothesis.

4 - the probability of rejecting a null hypothesis when in fact it is true.

5 - the chance of getting statistic as extreme or more extreme than this one

6 - the strength of evidence against an hypothesis

7 - the probability of the observed difference between groups (or a larger

difference) occurs

8 - the probability of obtaining a result equal to or more extreme than what

was actually observed.

9 - ....

10 - ...

What is the best way to explain this P = 0,79 ???

Thanks for any hints !!!

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Prof. J. C. VOLTOLINI

Grupo de Estudos em Ecologia de Mamiferos (ECOMAM)

Universidade de Taubate, Departamento de Biologia

Praca Marcelino Monteiro 63, Bom Conselho.

Taubate, SP. CEP 12030-010. BRASIL.

Tel: 0XX12 - 2254165 (Lab. Zool.) ou 2254277 (Depto. Biol.)

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"Tutto di noi è un angelo con un'ala e

possiamo volare soltanto se ci abbracciamo"