My response variable is continuous and ranges betwen 0.77 to 1.2.
I have 31 observations, 6 factors each at 3 levels. Its not a full
factorial, since that would require 729 runs. My full model contains
all the main effects (which would be 6 terms), the pair wise second
order interaction terms(which would be 15 terms) and the square terms ,
i.e. x1*x1 x2*X2 X3*X3 X4*X4 X5*X5 and X6*X6.
When I did the stepwise regression I was able to get rid of X1*X2 ,
X1*X3, X2*X5 , X4*X4 and X5*X5(I apologize the error in my post, which
says I was able to get rid of only 3 variables) So, I basically have 8
df for my error term.
Please let me know if I can further clarify.
I appreciate your response.
Thanks!
In article <[EMAIL PROTECTED]>,
Bob Wheeler <[EMAIL PROTECTED]> wrote:
> You haven't said anything about the response. It
> is obviously in the space spanned by the terms of
> the model. It could be something simple as the
> presence of exact replicates. (If it is truly
> D-optimal and if you truly used all 27 terms, then
> it must be a full factorial. Is it?)
>
> [EMAIL PROTECTED] wrote:
> >
> > Hi,
> >
> > I constructed a D-optimal design for 6 continuous variables, each at
> > three levels. I have 31 runs. My initial model includes, all the
main
> > effects, all interactions and polynomial terms. I was only able to
> > remove 3 of the terms using step wise regression, My final model
has an
> > R square of 0.9954, which looks very artificial. My adjusted R
square
> > is also very close to R Square. Does anyone have any suggestion on
what
> > could have gone wrong or if there is a different analysis technique
> > that I can use?
> > I even did a lack of fit test, and the interaction terms and square
> > terms were significant. I'll appreciate any help in this regard.
Thanks
> > for your help!
> >
> > Sent via Deja.com http://www.deja.com/
> > Before you buy.
>
> --
> Bob Wheeler --- (Reply to: [EMAIL PROTECTED])
> ECHIP, Inc.
>
Sent via Deja.com http://www.deja.com/
Before you buy.
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