Re: Retest estimation from the test-retest r?

Ray Koopman wrote:

scientia@xxxxxxxxxxx wrote:

[snip]
I don't know if there is a standard answer to this question, so
I tried to calculate it by myself, assuming that both the mean M2
and the standard deviation SD2 of the supposed retest are
approximately the same of the test, M and SD. I found:
sdp^2 = 2 * SP^2 * (1 - r)
Is this correct? And is it a well known result?

That is a standard well-known result.

Can I have a reference? I can't find this result anywhere.
Is it somehow related to a 1991 article by Jacobson and Truax?

Thanks

Fabrizio Coppola
Istituto Scientia
Italy

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