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From   Sarah Elaine Cabbage <cabbages@u.washington.edu>
To   statalist@hsphsun2.harvard.edu
Date   Mon, 28 Aug 2006 17:03:14 -0700 (PDT)

Hello,

I'm trying to do a permutation test in Stata and just can't seem to get the syntax right. Here's my command:

permute norm_qty permt=r(t), strata(group) : ttest norm_qty, by(group)

This is what I get in return:


Monte Carlo permutation results

Number of strata = 2 Number of obs = 10

command: ttest norm_qty, by(group)
permt: r(t)
permute var: norm_qty

------------------------------------------------------------------------------
T | T(obs) c n p=c/n SE(p) [95% Conf.Interval]
-------------+----------------------------------------------------------------
permt | -4.373186 100 100 1.0000 0.0000 .9637833 1
------------------------------------------------------------------------------
Note: Confidence interval is with respect to p=c/n.
Note: c = #{|T| >= |T(obs)|}


I'm trying to do a comparison of mean values of "norm_qty" between two groups with a small sample size. Why is it telling me that all my
permutations come out with the same T-statistic as the observed distribution?

Thank you very much for any help anyone can give me.


Sarah Cabbage
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