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# Re: st: RE: Zcalc - with different sd in two groups

 From Lars Folkestad To "statalist@hsphsun2.harvard.edu" Subject Re: st: RE: Zcalc - with different sd in two groups Date Thu, 14 Jul 2011 18:00:27 +0200

```Thank you.
Just to clarify x1bar = group 1 mean?
S1 is The sd of group 1?

Mvh

Den 14/07/2011 kl. 17.41 skrev "Lachenbruch, Peter" <Peter.Lachenbruch@oregonstate.edu>:

> Why not calculate it from the definition of the z-score?
> For common sd you have
> Z=(x1bar-x2bar)/s(sqrt(1/n1+1/n2))
> For different sd you have
> Z=(x1bar-x2bar/sqrt(s1^2/n1+s2^2/n2)
> It's a one line program either way.
>
> Tony
>
> Peter A. Lachenbruch
> Department of Public Health
> Oregon State University
> Corvallis, OR 97330
> Phone: 541-737-3832
> FAX: 541-737-4001
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Lars Folkestad
> Sent: Thursday, July 14, 2011 4:47 AM
> To: statalist@hsphsun2.harvard.edu
> Subject: st: Zcalc - with different sd in two groups
>
> Dear Stata list
>
> I have two groups with two means and different standard deviations (SD), and the latter is the problem.
> Using the zcalc program, se description below, i can calculate a z-score between the groups if the SD was the same in both groups.
>
> How do i calculate the normal value (z-score) for a measurement method when the groups have different means?
>
> Thank you
> Lars
>
> The zcalc option from findit:
> ---------------------------
> Description
> -----------
>
> zcalc is a silly little program that computes z-scores.
>        If you provide the arguements x mean sd, zcalc
>        computes a z-score for observations.  If you
>        provide the arguements mean mu sd n in the arguement
>        list zclac computes a z-score for sample means.
>
> ---------------------------------
>
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