Defining a treatment contrast

!CONTRAST

This qualifier provides a convenient way to define contrasts among treatment levels.
     !CONTRAST name factor contrast
definitions occur as separate lines between the datafile line and the model line.
     name is the name of the model term being defined.
     factor is the name of an existing factor.
     contrast is the list of contrast coefficients.

The contrast name can then be included as a term in the linear model and will represent 1 degree of freedom from the factor on which it is based.

Example

  !CONTRAST LinN Nitrogen {3 1 -1 -3}/10

defines model term LinN as a contrast based on the 4 (implied by the length of the list) levels of existing factor Nitrogen.

The user should check that the levels of the factor are in the order assumed by contrast (check the .ass, .sln or .tab files). Missing values in the factor become missing values in the contrast. Zero values in the factor (no level assigned) become zeros in the contrast.

Note that the actual contrast effect reported will depend on what else is in the model, and the F values recorded depend on the order terms are fitted, particularly when contrasts are not orthogonal.

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