Date:         Fri, 25 Feb 2011 10:53:09 -0600
Reply-To:     "Swank, Paul R" <Paul.R.Swank@uth.tmc.edu>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         "Swank, Paul R" <Paul.R.Swank@uth.tmc.edu>
Subject:      Re: Regression 2-way Interactions?
Comments: To: "Salbod, Mr. Stephen" <ssalbod@pace.edu>
In-Reply-To:  <B34E0630AAAB774CB8D290E4723BC0FE182834D7@FSMAIL1.pace.edu>
Content-Type: multipart/alternative;

No, you do not have to specify A*B if you have no reason to. However, sometimes interactions occur when we don't expect them.

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

From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] On Behalf Of Salbod, Mr. Stephen
Sent: Friday, February 25, 2011 10:25 AM
To: SPSSX-L@LISTSERV.UGA.EDU
Subject: Regression 2-way Interactions?


Good Afternoon Friends,

I have a question regarding two-way interactions in regression analysis. I have three variables (gender, A, B, the latter two are continuous variables). I am interested only in two 2-way interactions (gender*A, gender*B) out of three. I plan to enter at Step 1: gender; Step 2: A, B; Step 3: gender*A, gender*B. To test these 2-way interactions (R square change), do I need to include the A*B interaction too?

Any suggestion or references will be greatly appreciated.

Stephen Salbod, Pace University, NYC

[text/html]