# Follow up to stat question

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## Follow up to stat question

 Dear list:  A continuation of the evacuation question. I went ahead and looked at the time for evacuation (started to evacuate to exited onto the street). The correlations between floor started and time was .75 for one building and .77 for the other building. Next I did a regression analysis allowing for linear and quadratic. In both instances the linear and quadratic functions were significant. Next I allowed for a cubic function and this is what happened.  For building 1 Linear was significant, quadratic and cubic were not significant.  For building 2 linear was not significant, but quadratic and cubic were significant. My question is how would I lose significance for the quadratic when the cubic was allowed to enter for building 1. Also why would I lose significance for linear  (given the very large zero-order correlation-my expectation was that the linear would stay in) for building 2 while picking up the cubic (besides the quadratic). Befuddled.   TIA. P.S. A colleague recommended a Loess fitting curve. Does anyone have any thoughts about using the Loess? martin sherman
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## Re: Follow up to stat question

 Did you center the time variable before doing the analyses? Paul ________________________________ From: SPSSX(r) Discussion on behalf of Martin Sherman Sent: Sun 6/25/2006 11:02 AM To: [hidden email] Subject: Follow up to stat question Dear list:  A continuation of the evacuation question. I went ahead and looked at the time for evacuation (started to evacuate to exited onto the street). The correlations between floor started and time was .75 for one building and .77 for the other building. Next I did a regression analysis allowing for linear and quadratic. In both instances the linear and quadratic functions were significant. Next I allowed for a cubic function and this is what happened.  For building 1 Linear was significant, quadratic and cubic were not significant.  For building 2 linear was not significant, but quadratic and cubic were significant. My question is how would I lose significance for the quadratic when the cubic was allowed to enter for building 1. Also why would I lose significance for linear  (given the very large zero-order correlation-my expectation was that the linear would stay in) for building 2 while picking up the cubic (besides the quadratic). Befuddled.   TIA. P.S. A colleague recommended a Loess fitting curve. Does anyone have any thoughts about using the Loess? martin sherman
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## Re: Follow up to stat question

 In reply to this post by msherman > My question is how would I lose significance for the quadratic when the > cubic was allowed to enter for building 1. Also why would I lose > significance for linear  (given the very large zero-order correlation-my > expectation was that the linear would stay in) for building 2 while > picking up the cubic (besides the quadratic). Befuddled.   TIA. Did you test for multi-collinearity? The linear, quadratic and cubic evacuation time should be highly intercorrelated.
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## Re: Follow up to stat question

 Correlated, but not necessarily LINEARLY correlated. Hector -----Mensaje original----- De: SPSSX(r) Discussion [mailto:[hidden email]] En nombre de Marc Halbrügge Enviado el: Sunday, June 25, 2006 3:10 PM Para: [hidden email] Asunto: Re: Follow up to stat question > My question is how would I lose significance for the quadratic when the > cubic was allowed to enter for building 1. Also why would I lose > significance for linear  (given the very large zero-order correlation-my > expectation was that the linear would stay in) for building 2 while > picking up the cubic (besides the quadratic). Befuddled.   TIA. Did you test for multi-collinearity? The linear, quadratic and cubic evacuation time should be highly intercorrelated.
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## Delete me

 In reply to this post by Swank, Paul R It's too much. Delete me on your list. Thanks. J. Schoeters
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