[R] Manually Calculating Odds from POLR Model

From: Tate Avery <tate_sterling_avery_at_hotmail.com>
Date: Sat 13 Aug 2005 - 05:50:17 EST


Hello,

I am using polr(...) to generate a model. The summary shows the coefficients and the intercepts.

For example:

    coefficient for x1 = c1
    coefficient for x2 = c2

    intercept A|B = i1
    intercept B|C = i2

I can then run predict(..., type="p") with the model and see the odds for each factor.

For example:

      A        B        C
1    0.3     0.5      0.2
2    0.4     0.1      0.5

What I really want to be able to do is take the 2 coefficients, the 2 intercepts, the x1 & x2 values and manually calculate the probabilities generated by predict().

I have been searching quite extensively for the underlying calculations that transform the polr output and the input variables into the final output odds. I have tried a number of dead-end roads so far.

So, if anyone has any information on how to do this or where I can find out, I would be extremely grateful.

Thank you for your time,
Tate Avery



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