```Date: Mon, 19 May 2008 13:51:34 -0500 Reply-To: "Swank, Paul R" Sender: "SPSSX(r) Discussion" From: "Swank, Paul R" Subject: Re: regression - nonsig to sign Comments: To: "Zdaniuk, Bozena" In-Reply-To: Content-Type: text/plain; charset="us-ascii" There are two ways in which this can happen. First and most commonly, it is as Hector has said, the variables B & C relate to variability in the dependent variable (call it Y) that is not associated with A. Ten the effect of A stands out more once this other variance is removed. This is the reason we often have covariates in our models, the control for other sources of variation in Y. So we increase the power of our test on A. The other was is when B &/or C are related to A and reduce the extraneous variance in A that is not related to Y. This is often called a suppressor effect. Thus, it would help to look at the whole correlation matrix of A, B, C and Y to see how these variables interrelate. Paul R. Swank, Ph.D. Professor and Director of Research Children's Learning Institute University of Texas Health Science Center - Houston -----Original Message----- From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] On Behalf Of Zdaniuk, Bozena Sent: Monday, May 19, 2008 8:35 AM To: SPSSX-L@LISTSERV.UGA.EDU Subject: regression - nonsig to sign Hello, when I enter predictor A by itself into regression model, it is not significant. But if I add predictors B and C, predictor A becomes significant. How can I interpret it? thanks a lot. Bozena ________________________________________ ===================== 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 ===================== 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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