Date: Mon, 22 May 2006 10:49:52 +0200
Reply-To: Marta García-Granero
Sender: "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From: Marta García-Granero
Organization: Asesoría Bioestadística
Subject: Re: Degrees of Freedom in Excel
Content-Type: text/plain; charset=ISO-8859-15
PGP> I am trying to make an Excel file which replicates SPSS' independent
PGP> t-test procedures using means, standard deviations and sample sizes.
PGP> I've almost got it, but for some reason I seem unable to implement the
PGP> calculation for the degrees of freedom (Df) that SPSS uses when the
PGP> variances of the two samples differ significantly.
I wrote SPSS code for that (available at:
PGP> Does anybody know what this formula should look like in SPSS?
The formula for Welch DF that I know is this one:
(S²a/Na + S²b/Nb)²
--------- + ---------
Using it I get the same result (up to 3 decimal places) that the one
provided by T-TEST procedure.
You can find the description of Welch test and the formula here: