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Re: st: Chi-square test for Categorical Data Analysis
At 04:00 PM 9/18/2007, Maarten buis wrote:
> Second question - does the chi-square test convey any additional
> information other than the fact that the distributions are different?
> That is, since only the number of observations in each group is being
> tested, can I, for example, conclude that Group A is making
> significantly more income than Group B?
No, the Chi-square test just says that these distributions are
different. Again -intreg- will give you more meaningfull output.
Actually, since it is a 2 by 2 table, you can do a z-test with a
signed effect. See case II of
http://www.nd.edu/~rwilliam/stats1/Categorical-Stata.pdf
But note: this would just say that one group had significantly more
people above the median than the other group did. That isn't
necessarily the same as one group making significantly more
money. For example, one group might have relatively few people above
the median, but those people could be really really really rich. Or,
there might be no significant differences in % above the median, but
the above average people in one population could be a lot richer than
the above average people in the other population.
In the Stata reference manual for intreg, it gives an example along
the lines of what Martin later suggests, i.e. log the endpoints of income.
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Richard Williams, Notre Dame Dept of Sociology
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