[R] summary(polr.object)

[Tord Snall]

Dear all, 

I have used polr in MASS but I am uncertain about the summary(polr.object)
interpretation and would be happy for help on that. This is my summary:

> summary(shade.polr)

Re-fitting to get Hessian

Call:
polr(formula = as.ordered(shade) ~ as.factor(objekt), data = sof, 
    weights = as.numeric(frek))

Coefficients:
     Value Std. Error    t value 
 2.1699520  0.3681840  5.8936612 

Intercepts:
    Value   Std. Error t value
2|3 -2.2975  0.2656    -8.6500
3|4  2.8737  0.3296     8.7175

Residual Deviance: 347.5964 
AIC: 353.5964 


The ordered variable thus has 3 levels. The independent as.factor(objekt)
has two levels.

Is t=5.8936612 for a test of difference in the ordered response between the
two groups, and is the p-value for the two-sided test thus 
2* (1-pt(5.8936612, df=shade.polr$df.residual))

Why is the p-value not reported? Is there a special reason that would be
good to know?

Furthermore is t = -8.6500 in 
2|3 -2.2975  0.2656    -8.6500
for a test of difference in the proportion of twos and threes between the
two levels of the independet factor?

Is the p-value: 2* (1-pt(8.6500, df=shade.polr$df.residual))?


Thanks in advance!


Sincerely,
Tord Snäll

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Tord Snäll
Avd. f växtekologi, Evolutionsbiologiskt centrum, Uppsala universitet
Dept. of Plant Ecology, Evolutionary Biology Centre, Uppsala University
Villavägen 14			
SE-752 36 Uppsala, Sweden
Tel: 018-471 28 82 (int +46 18 471 28 82) (work)
Tel: 018-25 71 33 (int +46 18 25 71 33) (home)
Fax: 018-55 34 19 (int +46 18 55 34 19) (work)
E-mail: Tord.Snall at ebc.uu.se
Check this: http://www.vaxtbio.uu.se/resfold/snall.htm!
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