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Re: st: k-sample tests for differences in proportions


From   Richard Williams <Richard.A.Williams.5@nd.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: k-sample tests for differences in proportions
Date   Wed, 05 Nov 2003 07:17:59 -0500

At 09:18 AM 11/5/2003 +0000, klrobson@essex.ac.uk wrote:
Is there an established equivalent command to "prtest" for categorical
variables with more than two categories?

If not, just 'how wrong' is it to use an anova estimation for this purpose?

Thanks for any guidance.
I just tried the csgof command suggested by Ronan Conroy for a single variable, and it works as I would expect it to. In SPSS, you would use the NPAR test command for this purpose.

But, are you talking about comparing proportions between 2 variables, e.g. Var1 and Var2, each has 5 categories, and you want to test whether the proportion in each category is the same for each variable? If so, I don't understand why you would consider Anova, since you'd be computing means of a categorical variable. If csgof doesn't give you what you want, perhaps you could give a specific example of what it is you want to test.

Incidentally, I have "cheated" and used Anova to test p1=p2, where p1 is the proportion of successes in the first group and p2 is the proportion of successes in the 2nd group. That is, both my IV and DV were dichotomies. At least in the large samples I tried it on, I got almost exactly the same results you get by doing it the "right" way. But, once you get past 2 categories on your categorical dependent variable, Anova doesn't make any sense to me.


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