I would like to constrain three of the parameters I am estimating using sem (strucutral equation model package) but do not know how. Specifically, I would like to use the following constraint: beta1 + beta2 + beta3 = 1 can I assign variable names as the values for fixed parameters? If so, I could define the third parameter to be equal to 1 - beta1 - beta2. thanks, james ------------------------------------------------------------------------- James H. Fowler, Assistant Professor web: http://jhfowler.ucdavis.edu Department of Political Science email: jhfowler at ucdavis.edu University of California, Davis phone: (530) 752-1649 One Shields Avenue fax: (530) 752-8666 Davis, CA 95616