Hello, I'm attempting to extract a data set. I enter: 'mdata <- match.data(m.out)' after assigning 'm.out <- matchit(treat ~ x1...)' 'summary(mdata)' yeilds the following: distance.Length distance.Class distance.Mode NA.Length NA.Class NA.Mode weights 1 -none- function 1 -none- numeric Min. :1 1 -none- function 1 -none- numeric 1st Qu.:1 1 -none- function 1 -none- numeric Median :1 1 -none- function 1 -none- numeric Mean :1 1 -none- function 1 -none- numeric 3rd Qu.:1 1 -none- function 1 -none- numeric Max. :1 1 -none- function 1 -none- numeric In addition, I am unable to extract the dataset: write.dta(mdata, "mdata.dta") Error in write.dta(mdata, "mdata.dta") : unknown data type I am, however, able to view the results of the matching analysis, use the plot function, etc. Any idea what's going wrong? I am really just looking to observe which control observations were matched to my treatment observations. Is there an easier way to do this within R? If the manual helps on this point I am too dense to understand it because I've tried... Thanks, Alyssa PS: The commands work fine when I run the lalonde data.