Date:         Fri, 4 Aug 2006 08:51:00 -0400
Reply-To:     Jonas Bilenas <jonas.bilenas@CHASE.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Jonas Bilenas <jonas.bilenas@CHASE.COM>
Subject:      Re: Multiple regression help-dummy variables vs class variables

First questions I have is why do you want to convert duration, which seems
to be an interval or ratio number, into 52 dummy variables?  Have you
looked at the relationship between duration and your dependent variable?

Jonas Bilenas
JP Morgan Chase


On Thu, 3 Aug 2006 17:00:46 -0400, Karen Intrachat <intrachat@GMAIL.COM>
wrote:

>I am trying to predict the a stop rate given the Price Term Year and
>duration of the promotion.  I am using duration as a dummy variable.
>
>If i did a multiple regression using a variable named "dur" that has values
>0-52.
>
>If i make "dur" into a class variable and run my regression, will its
>coefficient estimates be different if did a regression and make "dur" a
>dummy variable "dur0-dur52".
>
>Is this true? what is the difference?
>
>also what if i want to use an interaction term...
>how do i use it in my model...ie...
>
>proc glm data=data;
>  model stop= price term dur1 dur2  dur1*term  dur2*term
>end;
>
>where dur1 and dur2 are dummy variables....i am given coeffiecient
>estimates...and lets say price=1 term=2
>
>is this what i do?
>
>stop for dur1=1:  stop = b1*(1) + b2*(2) + b3*(1) + b4*(0) + b5*(1)*(2) +
>b6*(0)*(2)
>
>or for the dur1*term interaction terms...would i have to on the side
>multiply  duration*term...so would the equation be this given the table
>below
>
>duration term  --> duration*term
>1             2               (1*2)
>2             2                (2*2)
>
>then would my equation be
>
>stop= b1*(1) + b2*(2) + b3*(1) + b4*(0) + b5*(1*2) + b6*(2*2)?
>
>For some reason when i have been getting a very bad Rsquared value when i
do
>these regressions...and most of the time the coefficient estimates have
high
>pvalues.  if I set their coefficient estimates to zero for duration, then
my
>model is not very reflective of what is going on...does anyone have
>suggestions?