Multidimensional metric unfolding with SMACOF

December 12, 2012

(This article was first published on is.R(), and kindly contributed to R-bloggers)

SMACOF stands for “Scaling by MAjorizing a COmplicated Function,” and it is a multidimensional scaling algorithm for metric unfolding of, among other things, rectangular ratings matrices.

One neat Political Science application of MDS is inferring ideology from survey thermometer ratings. The 2008 ANES featured 43 different thermometer stimuli, and today’s Gist shows how to use SMACOF to simultaneously scale survey respondents and thermometer stimuli in the same space, and to compare this measure of inferred ideology across partisans.

I’ve also got a little piece of code that replaces numeric axis labels with names of the stimuli, which I think might be better, as the numbers don’t really mean much except in comparison with the stimuli. Let me know what you think!

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