GLM Syntax - Example 7: Mixture Design

This example illustrates the specification for a mixture surface design. You can run this example with the example data file Fish.sta. Two alternative Design specifications are shown; one using the @  and | (bar) operator shortcuts, the other with the terms of the response surface model explicitly written out. For a discussion of this data set and analyses, see also the example mixture design described in the context of the Experimental Design module. Note that brief descriptive comments are enclosed in curly brackets.

GLM;

{ Dependent variable list: }

   DEPENDENT = TEXTURE;

{ The mixture components are specified as continuous predictors. }

   COVARIATE = MULLET SHEEPSHD CROAKER;

   DESIGN =  MULLET | SHEEPSHD | CROAKER @2;

{ An alternative Design specification without the use of the @ and | operators is:

   DESIGN = MULLET + CROAKER + SHEEPSHD +

            MULLET*SHEEPSHD + MULLET*CROAKER + SHEEPSHD*CROAKER; }

{ The intercept is excluded from the model because of the mixture

   constraint; see Experimental Design for details. }

   INTERCEPT = EXCLUDE;

{ The next statement "flags" the three continuous predictors as mixture components. }

   MIXTURE = MULLET SHEEPSHD CROAKER;

For more examples, see GLM Syntax Examples.

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