We have MASS and Zelig in there because some functions are borrowed from those packages. MASS is a standard package, and so i don't think it's a big problem to require it. And, some of us including myself hope that Zelig will become a standard package in the future! :) As for the requirement of R 2.2.0, we do it simply because we only test it against the most recent version of R. Some functions are not backward compatible because R is not generally not backward compatible. Kosuke ----------------------------------------------------- Kosuke Imai Office: Corwin Hall 041 Assistant Professor Phone: 609-258-6601 Department of Politics eFax: 973-556-1929 Princeton University Email: kimai(a)Princeton.Edu Princeton, NJ 08544-1012 http://imai.princeton.edu ----------------------------------------------------- On Wed, 30 Nov 2005, David Kane wrote: - MatchIt mailing list served by Harvard-MIT Data Center List Address: matchit(a)latte.harvard.edu Subscribe/Unsubscribe: http://lists.hmdc.harvard.edu/?info=matchit MatchIt Software and Documentation: http://gking.harvard.edu/matchit/