Response Surface Analysis

Im trying to do a response surface analysis using SAS but am somewhat
confounded. Ive taken a number of stat classes but will be the first to
admit that
Im rather weak when it comes to experimental designs and linear models.

Im working with three numeric variables x1, x2, x3 and a number of response
variables. I gathered data using a circumscribed central composite design.

Ive been using proc rsreg but am not entirely sure how to go about
interpreting the data and in what order to interpret it. On the offchance
of
interest here is some sample output:
http://www.id.unizh.ch/software/unix/statmath/sas/sasdoc/stat/chap56/sect5.htm

My understanding is to look at the pvalues for each of the 9 (10 with
intercept) coefficients and build your model/response surface from that.

Then look at the eigenvalues to check to see if its the expected optimum.
If its not the expected optimum(saddlepoint for instance), or if the
expected
optimum is occuring at x values far outside the specified range then I need
to use the ridge command to 'recalibrate' and run the study again.

Im not certain of how to interpret the tests on linear/quadratic/crossterm.
Do I only consider checking the pvalues of the linear
coefficients if the linear test is significant? Same with quadratic and
crossterm? For instance I think I have one dependent variable where
the crossterm test is insignificant but x1*x3 is significant. Should that
be ignored?

What can or should be done if the lack of fit is significant?

How does one interpret/use/ignore the 4 df tests on x1, x2, x3?

Finally what if my model says that, for instance, x1 and x2 are significant
but x3 is not. Then when I look at the eigenvalues I have
positives for x1 and 2 and negative for x3. Since Im not including x3 would
this no longer be a saddlepoint? Would it now be
a minimum? Or should I still follow the ridge suggestions and run more
experiments?

Answers to any questions, of any shallowness or depth are dearly
appreciated. Im rather groping blindly and could use any sort
of pity/help that the statistical cosmos has to offer.

Best regards,
--Scott


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Relevant Pages

  • Response Surface Analysis
    ... Im trying to do a response surface analysis using SAS but am somewhat ... Im rather weak when it comes to experimental designs and linear models. ... Im not certain of how to interpret the tests on linear/quadratic/crossterm. ... the crossterm test is insignificant but x1*x3 is significant. ...
    (sci.stat.consult)
  • Response Surface Analysis
    ... Im trying to do a response surface analysis using SAS but am somewhat ... Im rather weak when it comes to experimental designs and linear models. ... Im not certain of how to interpret the tests on linear/quadratic/crossterm. ... the crossterm test is insignificant but x1*x3 is significant. ...
    (sci.stat.edu)