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Re: st: Numerous t-tests

From   Roger Newson <>
Subject   Re: st: Numerous t-tests
Date   Wed, 26 Oct 2005 12:03:13 +0100

At 11:32 26/10/2005, Allan wrote:
I have what should be a very simple question, but I haven't been able to figure out the answer. I want to do group mean comparison t-tests and rank sum tests on a number of different variables.. But, it appears that both -ttest- and -ranksum- will only do 1 variable at a time. So, is there a single command that will let me put in any number of variables (along with the 2-level grouping variable, of course) and will then do ALL the tests at once?
You might want to use the -somersd- package, downloadable from SSC, to calculate confidence intervals for Somers' D and the Hodges-Lehmann median difference (corresponding to the ranksum test). For instance, if you type

somersd group y1 y2 y3 y4, tr(z)

then -somersd- will output confidence intervals for the Somers' D of the variables -y1-, -y2-, -y3 -and -y4- with respect to the grouping variable -group-.

Confidence intervals are usually more informative than P-values alone. For more about confidence intervals corresponding to rank statistics, see Newson (2002).

I hope this helps.

Best wishes



Newson R. 2002. Parameters behind "nonparametric" statistics: Kendall's tau, Somers'
D and median differences. The Stata Journal 2(1): 45-64. Pre-publication draft
downloadable from Roger Newson's website at

Roger Newson
Lecturer in Medical Statistics
Department of Public Health Sciences
Division of Asthma, Allergy and Lung Biology
King's College London

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