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Date:         Tue, 13 May 2008 15:43:23 -0500
Reply-To:     Anthony Babinec <tbabinec@sbcglobal.net>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Anthony Babinec <tbabinec@sbcglobal.net>
Subject:      Re: interaction in multinomial logistic
In-Reply-To:  <C9563A8511C9BB488B41E541ACC749F95E85C5A484@PITT-EXCH-07.univ.pitt.edu>
Content-Type: text/plain; charset="US-ASCII"

On the face of it, A should have one redundant parameter and the A*B interaction should have one redundant parameter. This comes about because of NOMREG's "set to 0" parameterization of categorical variables. Double-check the messages to see whether this is not in fact the case. Just speculating - Instead of a stepwise method, try enter. If the A*B interaction is in the model, you usually want the respective main effects in, and this is not guaranteed with stepwise. Also, re-write the MODEL statement to list A*B last.

-----Original Message----- From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] On Behalf Of Zdaniuk, Bozena Sent: Tuesday, May 13, 2008 12:16 PM To: SPSSX-L@LISTSERV.UGA.EDU Subject: interaction in multinomial logistic

Hello, I am running a multinomial logistic with factor predictor A (three categories), continuous predictor B and an interaction term A*B. (syntax below). For some reason, the results do not show the main effect for B ("this parameter is set to zero because it is redundant"). I have hard time understanding why it is redundant. When running similar model in binary logistic regression, I do get all the main effects. Anybody willing to share some wisdom on that? thanks so much. Bozena

NOMREG grouping (BASE=FIRST ORDER=ASCENDING) BY A WITH B C D /CRITERIA CIN(95) DELTA(0) MXITER(100) MXSTEP(5) CHKSEP(20) LCONVERGE(0) PCONVERGE(0.000001) SINGULAR(0.00000001) /MODEL= A*B A B C D /STEPWISE = PIN(.05) POUT(0.1) MINEFFECT(0) RULE(SINGLE) ENTRYMETHOD(LR) REMOVALMETHOD(LR) /INTERCEPT =INCLUDE /PRINT = PARAMETER SUMMARY LRT CPS STEP MFI .

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