[R-sig-teaching] Interpreting the results

[Paul Johnson]

There appears to be a little mistake in your code

On Wed, Oct 3, 2012 at 3:57 PM, Ali Zanaty <zanaty2005 at yahoo.com> wrote:
> Dear All:
> I have two variables:
> X (nominal categorical) has 9 categories.
> Y(ordinal categorical) has 4 categories.
>
> 1-I fit a logistic regression using Y as
> the response variable and X as the independent variable. The P VALUE was
> 0.2373. This tells me that the independent variable X is NOT significant
> predictor.
>

if X is nominal with 9 categories, the fitted regression should
include an intercept and 8 categories.  If it is only fitting one
predictor, that means  your X is not properly understood as a factor
variable.

If y is ordinal, then fitting the model requires use of some addon
package, not something provided with R. You'd need polr, ordinal, or
lrm from the rms package.

So I think you don't have what you think you have, and you'd better
double check and then post the full code for the model along with the
output of str() on your data frame.

pj

>
> 2- I run a
> chi-square test to test if there is a relationship (association ship) between
> both X and Y variables. The P VALUE was 0.0013. That is there is statistical
> evidence of association between the two variables.
>
> 3- I collapsed the 4 categories of the Y-variable into 2 categories. I run a
> chi-square test to test if there is a difference(s) among proportions of the X-variable (the equality of the 9 proportions). The P VALUE was 0.0037. That is there is statistical
> evidence of differences among the 9 proportions.
>
> How
> I can explain results of one versustwo, and one versus three. I am not sure if there is a contradiction among these results.
>  many
> thanks
> Ali
>         [[alternative HTML version deleted]]
>
>
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-- 
Paul E. Johnson
Professor, Political Science    Assoc. Director
1541 Lilac Lane, Room 504     Center for Research Methods
University of Kansas               University of Kansas
http://pj.freefaculty.org            http://quant.ku.edu