Date: Sun, 25 Jun 2006 12:02:17 -0400
Reply-To: Martin Sherman <MSherman@loyola.edu>
Sender: "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From: Martin Sherman <MSherman@loyola.edu>
Subject: Follow up to stat question
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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?