I am running R 2.3.1 on Linux and using MatchIt version 2.2-10. I'm having a problem similar to the one documented by David Kane on April 18th (See http://lists.hmdc.harvard.edu/lists/matchit/2006_04/msg00004.html). It seems that when I include a column of class "character" in the data frame that I pass as an argument to "data", the "summary" method returns the following error: Error in x * w : non-numeric argument to binary operator In addition: Warning messages: 1: argument is not numeric or logical: returning NA in: mean.default(x1, na.rm = T) 2: argument is not numeric or logical: returning NA in: mean.default(x0, na.rm = T) I replicated the error using the toy example that Dave Kane provided: treated b c Min. :0.00 Min. :-1.9144 blue :50 1st Qu.:0.00 1st Qu.:-0.6510 green:50 Median :0.00 Median :-0.1772 Mean :0.11 Mean :-0.0378 3rd Qu.:0.00 3rd Qu.: 0.5009 Max. :1.00 Max. : 2.3080 Error in x * w : non-numeric argument to binary operator In addition: Warning messages: 1: argument is not numeric or logical: returning NA in: mean.default(x1, na.rm = T) 2: argument is not numeric or logical: returning NA in: mean.default(x0, na.rm = T) Subsequently, I set the "c" column of "x" to all 0s, called "matchit" again, then called called summary. There were no errors under this configuration. As I mentioned earlier, the problem most likely has to do with the multiplication of character data. I would lke to use "character" values as pre-treatment variables so a solution to this problem would be greatly appreciated! Thank you! Daniel Gerlanc - MatchIt mailing list served by Harvard-MIT Data Center List Address: matchit(a)lists.gking.harvard.edu Subscribe/Unsubscribe: http://lists.gking.harvard.edu/?info=matchit MatchIt Software and Documentation: http://gking.harvard.edu/matchit/