Not GLM, but MIXED can do fixed effect models too.  Look at the PDIFF option on the LSMEANS statement and look at the new LSMESTIMATE statement that allows you to frame statistical estimates in terms of LS-means instead of parameter estimates.  That statement allows you to get the SE of some complicated combinations of LS-means. ... View more

Thanks 1zmm, I appreciate Steve and 1zmm working through this problem.   As many statisticians know, GENMOD, GLIMMIX etc., are great (potential) tools but if you can't extract a useful answer from the model, the technology is essentially useless.   Maybe ilink will be fixed some day, but in the meantime your fix is very insightfull.   I can get the difference in means by a simple subtraction;  and now, having a way to compute the std err makes it possible to create correct confidence intervals--everything you need for reporting a result. Thanks everyone. Ron Levine ... View more