Dear Matchit list, I am using matchit for my work, and I really appreciate the excellent work you have done so far. I have a question : I perform a nearest neighbor matching procedure with a large dataset ( 40 000 individuals, 15 variables) and when I use the standard propensity score as a distance, everything works fine : the matching is quite good However if I specify the "mahalanobis" distance I get an error saying that : "Lapack dgesv : le système est exactement singulier" (the system is exactly singular)... Do you have an idea of what might cause this problem ? I have no missing data... Many thanks - --- MatchIt mailing list served by HUIT List Address: matchit(a)lists.gking.harvard.edu Subscribe/Unsubscribe: http://lists.gking.harvard.edu/mailman/listinfo/ei MatchIt Software and Documentation: http://gking.harvard.edu/matchit/ Browse/Search List Archive: http://lists.gking.harvard.edu/mailman/private/matchit/ Matchit mailing list Matchit(a)lists.gking.harvard.edu https://lists.gking.harvard.edu/mailman/listinfo/matchit