#  Sequential Ideal Points 

 





January 09, 2010

 

 

Simon Jackman [puts together a plot](http://jackman.stanford.edu/blog/?p=1516) of how the estimation of ideal points of the 111th U.S. Senate changes as he adds each roll call. Every Senator starts the term at 0 and then branches out. It illustrates an interesting feature of these IRT models:

> The other thing is that there doesn't seem to be any obvious "vote 1? update for ideal points. That is, there is no simple mapping from the ideal point estimate based on m roll call to ideal point estimates based on m+1 roll calls. You have to start the fitting algorithm from scratch each time (and hence the appeal of exploiting multiple cores etc), although the results from the previous run giving pretty good start values.

Posted by [Matt Blackwell](http://www.iq.harvard.edu/blog/sss/archives/author/matt-blackwell/) at January 9, 2010 3:57 PM



 

 

 



 

 

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