I thought you couldn't have zeroes in a gamma distribution?

Paul R. Swank, Ph.D. Professor and Director of Research Children's Learning Institute University of Texas Health Science Center - Houston

-----Original Message----- From: SAS(r) Discussion [mailto:SAS-L@LISTSERV.UGA.EDU] On Behalf Of Amy Smith Sent: Monday, May 05, 2008 4:53 PM To: SAS-L@LISTSERV.UGA.EDU Subject: Is it true that a zero-inflated Gamma model is not possible in either GENMOD or NLMIXED?

Has anyone found a procedure in SAS for creating a zero-inflated Gamma model? My response variable is cost. I have a class variable called group that has three levels Intervention1, Intervention2, and Control. The following two models succeed without any problem. PROC GENMOD; CLASS group; MODEL cost = group / LINK=log DIST = bin; PROC GENMOD; CLASS group; MODEL cost = group / LINK=log DIST = gamma; I cannot figure out how to get GENMOD to join these to give a zero-inflated gamma model. Or I thought maybe NLMixed could handle this model but I cannot get the syntax to work right and I'm now questioning if it is even possible. Has anyone ever written SAS code that successfully runs on a zero-inflated gamma? I would really love to see the syntax on a simple example like I have here. Thanks for your help!

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