```Date: Thu, 22 Jan 2009 10:08:25 -0500 Reply-To: Gene Maguin Sender: "SPSSX(r) Discussion" From: Gene Maguin Subject: Re: Curvilinear regression Comments: To: Talk Stats In-Reply-To: <200901220541.n0LMeDgw005916@malibu.cc.uga.edu> Content-Type: text/plain; charset="US-ASCII" Angela, Ok, it sounds like you have two unconnected questions, one about mediators and one about moderators. I disagree with your characterization of your basic model x -> y as 'curvilinear', given that x is categorical. Your anova showed a main effect for x and either planned comparisons or post hoc tests showed that x(1) differed from x(2) and from x(3). That is not curvilinear. Curvilinear implies to me that x is (quasi-) continuous variable having, for example, a power relationship (x squared) with y. You don't have that. Ok. Moderation is easier to do. (Let me also suggest that you take a reading cruise through some good regression texts.) I'd suggest that you center your moderator, V, by subtracting its mean prior to use in the regression. This will minimize collinearity issues. Next, construct the product of x and V. Since X is categorical with three levels, you'll need to construct two contrast variables, xc2 and xc3, such that xc2 represents the x(2) vs x(1), x(3) contrast and xc3 represents the x(3) vs x(1), x(2) contrast. Then construct product variables for the xc2-V and xc3-V products. Now run your regression. Mediation. You definitely need to some background reading. The classic is Baron and Kinney from the early 1980's. But, the current leaders in mediation are David McKinnon and somebody whose name I can't think of at the moment. Perhaps somebody else will name the person. Anyway, this is a good google topic. Gene Maguin >>I am wondering who can give me the exact and very specific (fool proof) steps on SPSS how to run regressions to test my curvilinear model and my mediators( two continuous variable M1 and M2) 1.I ran anova before and am pretty sure there is a curvilinear relation between my x and Y. my x is a catergorical variable with three levels , I coded it using two dummies. 2.. I also have a moderator variable(v) continuous) supposedly to interact with x and jointly influencing Y? Any help on the steps to test 1. main effect of X on the curvilinear 2. interaction between x and moderatorV? 3. steps to test mediation (two mediators) 4. I also want graphs on interaction.... ===================== To manage your subscription to SPSSX-L, send a message to LISTSERV@LISTSERV.UGA.EDU (not to SPSSX-L), with no body text except the command. To leave the list, send the command SIGNOFF SPSSX-L For a list of commands to manage subscriptions, send the command INFO REFCARD ```

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