[R] OT: Predicted probabilities from ordinal regressions
Andrew Perrin
clists at perrin.socsci.unc.edu
Fri May 11 21:05:48 CEST 2007
Sorry if this is too off-topic, as we may not implement this in R
(although we may do so).
A student of mine is looking at some public opinion data in which there
appears to be a statistically significant difference between levels of
support for a proposal based on which of two question wordings is used.
That is, roughly half the sample was asked the question with wording 1,
the other half with wording 2, and the difference is large enough to be of
interest (approx. 6 percentage points different with an N of about
30,000).
The question is how best to model this. In the past I have generated
predicted probabilities based on the sample asked wording 1, used these to
assign those asked wording 2 to predicted categories, and used a logistic
regression to predict difference between predicted and actual response. In
this case, though, the question of interest uses a four-level ordinal
response, so ordinary predicted probabilities based on, e.g., and ordinal
logistic regression generate literally probabilities of being in each of
the four categories. Transforming this outcome into a prediction of
membership in one of the given categories is not straightforward. Can
anyone provide some insight into how to model predicted vs. actual
outcomes on an ordinal scale?
Thanks.
----------------------------------------------------------------------
Andrew J Perrin - andrew_perrin (at) unc.edu - http://perrin.socsci.unc.edu
Assistant Professor of Sociology; Book Review Editor, _Social Forces_
University of North Carolina - CB#3210, Chapel Hill, NC 27599-3210 USA
New Book: http://www.press.uchicago.edu/cgi-bin/hfs.cgi/00/178592.ctl
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