Hi All, Thank you so much for all of your helpful advice! I've imported a distance measure into MatchIt and when I try to use it for matching I receive the following message: Warning message: In if (distance %in% c("GAMlogit", "GAMprobit", "GAMcloglog", "GAMlog", : the condition has length > 1 and only the first element will be used It looks as though MatchIt thinks I'm trying to use generalized additive models to estimate the distance measure. However, when I list the variables in my data set, MatchIt lists the propensity score that I read in as the "distance". Data set also includes a variable called "weights" that's equal to one for all observations. My imported distance measure ranges from 0.007 to 0.9479. I'd appreciate any advice you may have on what this message means and how to address it so that I can match. Thanks again for your help. Best wishes, Sharon Simonton