FMARGINALTERMS procedure

Determines the marginal terms for the terms in a model formula (R.W. Payne).

Options

TERMS = formula	Terms whose marginal terms are required
FACTORIAL = scalar	Limit on the number of factors in the terms; default * i.e. no limit
INDIVIDUALTERMS = pointer or formulae	Saves the individual terms from the TERMS formula
DROPPABLE = variate	Contains 1 or 0 according to whether or not each term can be dropped from the TERMS formula
MARGINALTERMS = pointer or formulae	Marginal terms for each term in the TERMS formula
MARGINALTERMS = variate	The number of marginal terms for each term in the TERMS formula

Parameters

No parameters

Description

FMARGINALTERMS is useful when you want to decide on the strategy for testing the terms in a model formula. The formula is specified by the TERMS option. The individual terms that it defines can be saved by the INDIVIDUALTERMS option, in a pointer containing a model formula for each term.

FMARGINALTERMS can tell you which terms can be dropped once they have all been fitted. These are the terms that are not marginal to any other term in the model. For example, in the model formula A*B*C, which expands to

A + B + C + A.B + A.C + B.C + A.B.C

The term A cannot be dropped as it is marginal to A.B, A.C and A.B.C. Another example is that B.C cannot be dropped as it is marginal to A.B.C. The only term that can be dropped is A.B.C. This information can be saved by the DROPPABLE option, in a variate with a value for each term containing one if the term can be dropped or zero otherwise.

The MARGINALTERMS option can save a pointer, with a model formula for each term, containing the terms that are marginal to that term. The NMARGINALTERMS option saves a variate containing the number of terms marginal to each term.

 

Options: TERMS, FACTORIAL, INDIVIDUALTERMS, DROPPABLE, MARGINALTERMS, NMARGINALTERMS

Parameters: None

See also

Directives: FCLASSIFICATION

GenStat Reference Manual 1 Summary section on: Calculations and manipulation.

Example

CAPTION   'FMARGINALTERMS example'; STYLE=meta
FMARGINALTERMS [TERMS=A*B*C*D; INDIVIDUALTERMS=term; DROPPABLE=drop;\
               MARGINALTERMS=marginal; NMARGINALTERMS=nmarginal]
FOR [INDEX=i; NTIMES=NVALUES(drop)]
  PRINT        [SQUASH=yes; ORIENT=across] term[i]
  PRINT        [SQUASH=yes] nmarginal$[i],'marginal terms; droppable',drop$[i],'.';\
                FIELD=1; DECIMALS=0; SKIP=0,1,1,0
  IF nmarginal$[i].GT.0
    PRINT      [SQUASH=yes] marginal[i]
  ENDIF
  SKIP         [FILE=output] 1
ENDFOR