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SAS PROCEDURE for ANALYSIS OF VARIANCE

PROC GLM;

1.  Purpose: compare means obtained from an ANOVA design 
            
2.  Syntax:
            
    PROC GLM data=data set name ;
	   CLASS      vars ;
	   MODEL      dep var=effects ;
	   MEANS      effects/options ;
	   TEST       H=effects  E=error ;
	   MANOVA     H=effects  E=error ;
	   REPEATED   vars ;
	   BY         classification vars ;	
            
3.  Simple Main Effects
            
    PROC GLM;
	   CLASS A B C;
	   MODEL Y=A B C;
            
4.  Interaction and Main Effects
		
	   PROC GLM;
	   CLASS A B C;
	   MODEL Y=A B C  A*B
              B*C  A*C  A*B*C;					 
    (or MODEL Y=A|B|C;)
            
5.  Nested Effects
            
	   PROC GLM;
	   CLASS A B C;
	   MODEL Y=A B C(A B);	
            
6.  MEANS effects/options;
            
	   Options are :
	   TUKEY        =  HSD or WSD procedure
	   SCHEFFE      =  Scheff`e procedure
	   BON          =  Bonferroni t-test
	   SIDAK        =  Dunn-Sidak pairwise procedure
	   DUNNETT('j') =  The Dunnette procedure where j=control group
	   SNK          =  Newman-Keuls procedures			
	   LSD          =  least significant differences
	   CLDIFF       =  95% Confidence interval		
	   ALPHA        =  significance level
		                (default = .05)
	
 
	   For Example,
            
	   MEANS     A   B   A*B/ SNK ALPHA = 10;
            
	   will perform the Newman-Keuls test, at a = 10%, of group 
      mean differences on A and B main factors.  The A*B 
      interaction generates all of cell means without actually 
      testing them.
            
            
 7.  The PROC GLM also allows us to test planned <orthogonal or 
     nonorthogonal> contrasts by using the CONTRAST statement.    
     The general syntax is
            
		CONTRAST 'label'   effect     coefficients;
            		
     For example,
            
     CONTRAST  'A LINEAR & QUADRATIC'
                  A  -2  -1   0   1  2,
                  A   2  -1  -2  -1  2;
            
     will carry out two trend analyses, one on the linear trend 
     of Factor A and the other on the quadratic trend of Factor A.
            
            
     In order to carry out a test on the interaction term, such as 
     A*B, you need at least four cell means.  The following are two 
     orthogonal contrasts tested by the CONTRAST statements:
            
     CONTRAST 'The first and the second contrasts'
                 A*B   1 -1   0    -1   1   0,
                 A*B  .5 .5  -1   -.5  -.5  1;
            
            
     CONTRAST statement should be placed anywhere after PROC GLM, 
     CLASS, and MODEL statements.



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