Date: Fri, 9 Jun 2006 18:35:56 -0400 Reply-To: Kevin Roland Viel Sender: "SAS(r) Discussion" From: Kevin Roland Viel Subject: Re: additive effects: contrast? In-Reply-To: <6250203B042D8349A920AA6103830936015CE40E@UTHEVS3.mail.uthousto n.edu> Content-Type: TEXT/PLAIN; charset=US-ASCII On Fri, 9 Jun 2006, Swank, Paul R wrote: > have you tested for deviations from linearity? If so and there are none, > then you can say the indication is that the relation is linear. Then the > difference is b between each level and 2b between -1 and 1. By "deviations from linearity" do you mean an alternative to the -1, 0, 1 coding? If so, I have not. It is the response we expect theoretically and the coding I wish to test. Thanks, Kevin > Paul > > Paul R. Swank, Ph.D. > Professor, Developmental Pediatrics > Director of Research, Center for Improving the Readiness of Children for > Learning and Education (C.I.R.C.L.E.) > Medical School > UT Health Science Center at Houston > > -----Original Message----- > From: SAS(r) Discussion [mailto:SAS-L@LISTSERV.UGA.EDU] On Behalf Of > Kevin Roland Viel > Sent: Friday, June 09, 2006 4:24 PM > To: SAS-L@LISTSERV.UGA.EDU > Subject: additive effects: contrast? > > Greetings, > > In a multiple linear regression analysis, I have coded a covariate -1, > 0, and 1. Supposed the estimate is a (p=b). > > The interpretation is that that the mean of my outcome in the group > with 0 is a units higher than the mean in the group with -1. The same > is true for the group with 1 compared to the group with 0. For either, > I can say that p=b. > > The mean in the group with 1 is 2a higher than the mean in the group > with -1. It seems to me that I cannot say that p=b, in this case. > Maybe. > > Would it be best to use a CONTRAST statement in this situation. > > Thanks, > > Kevin > > > Kevin Viel > Department of Epidemiology > Rollins School of Public Health > Emory University > Atlanta, GA 30322 > Kevin Viel Department of Epidemiology Rollins School of Public Health Emory University Atlanta, GA 30322

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