Dear Toby, I encountered a similar problem a couple of months ago. I have never really understood how and why this error occurred, but in my case there was a problem in extracting singular variables from the data matrix (all). Perhaps you could try the following: # Ask for the dimensions of the data matrix dim(all) # Use these dimensions to manually create the dimensions of your matrix allr <- all[1:4032,1:19] # the dimensions I used are only an example, use the dimensions you get from R Subsequently, run the matchit code again. In my case it worked.... my two cents, Peter Lugtig ------------------------------ *From:* owner-matchit_at_lists_gking_harvard_edu(a)mail.hmdc.harvard.edu[mailto: owner-matchit_at_lists_gking_harvard_edu(a)mail.hmdc.harvard.edu] *On Behalf Of *Toby Edison *Sent:* Friday, July 24, 2009 4:30 AM *To:* matchit(a)lists.gking.harvard.edu *Subject:* [matchit] match.data undefined columns selected error I am having a problem getting the match.data function to work on my data. Just getting started with matchit, but cannot seem to get the match.data function to work on my data. I am using a Mac. Here is the code I use: all<-read.table("file:///all.txt", header = TRUE, sep = "\t", quote="\"", dec=".") m.out <- matchit(wins03 ~ firstcontractyear + foundingyear + employees + top_no + sub03 + prime03 + tns2002 + ts2002+ phiiawards + phiawards + cai, data = all, method = "cem") m.data <- match.data(m.out) z.out1<-zelig(tns05 ~ wins03+ tns2002 + ts2002 + tns03 + foundingyear + employees + sub03 + prime03 + phiiawards + phiawards + cai, data = m.data, model="ls") resulting in : Error in `[.data.frame`(d, , all.vars(as.expression(formula))) : undefined columns selected match.data works fine with the lalonde data set but I cannot get it to work with my imported data. I've saved my data from an excel spreadsheet into a tab delimited text file. I've tried using .csv imports as well. Any ideas. Toby Edison