question about plot.ci for probit/logit with dummy interaction - Zelig

9 Mar 2009

Hi - I am having the following problem with the plot.ci method:

[note that pspend_total is the total spending,
            incumb is 0 or 1 depending on incumbent or challenger]

...
  z.out <- zelig(wonseat ~ pspend_total*incumb+m,
model="probit",   data=dail)
How to cite this model in Zelig:
Kosuke Imai, Gary King, and Oliva Lau. 2007. "probit: Probit  
Regression for Dichotomous Dependent Variables" in Kosuke Imai, Gary  
King, and Olivia Lau, "Zelig: Everyone's Statistical Software,"
http://gking.harvard.edu/zelig
...
  x.incumb <- setx(z.out, pspend_total=1:30,
incumb=1, m=4)
 x.chall <- setx(z.out, pspend_total=1:30, incumb=0, m=4)
 s.out <- sim(z.out, x=x.incumb, x1=x.chall)

 plot.ci(s.out, xlab="% Candidate Spending in Constituency", +        
ylab="Probability of Winning a Seat")
Error in plot.ci(s.out, xlab = "% Candidate Spending in  
Constituency",  :
    x and x1 in vary on different dimensions.

Any ideas before I have to dig in and compute this from the return  
values of sim()??  Help much appreciated!

Ken

Kenneth Benoit
Professor of Quantitative Social Sciences
Head, Department of Political Science
Trinity College
Dublin 2, Ireland
http://kenbenoit.net
Tel: 353-1-896-2491

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