Define contrast in SPSS

 

The following contrast types are provided in SPSS

Indicator
Contrasts indicate the presence or absence of category membership. By default, Reference group is the first category (represented in the contrast matrix as a row of zeros).

Deviation
Compares the mean of each level (except a reference category) to the mean of all of the levels (grand mean). The levels of the factor can be in any order. Reference group allows you to select either the first or last group as the reference. The Preview pane displays information based on your selection.

Simple
Compares the mean of each level to the mean of a specified level. This type of contrast is useful when there is a control group. Reference group allows you to select either the first or last group as the reference. The Preview pane displays information based on your selection.

Difference
Compares the mean of each level (except the first) to the mean of previous levels. (sometimes called reverse Helmert contrasts). The Preview pane displays additional information regarding the selected contrast factor.

Helmert
Compares the mean of each level of the factor (except the last) to the mean of subsequent levels. The Preview pane displays additional information regarding the selected contrast factor.

Repeated
Compares the mean of each level (except the last) to the mean of the subsequent level. The Preview pane displays additional information regarding the selected contrast factor.

Polynomial
Compares the linear effect, quadratic effect, cubic effect, and so on. The first degree of freedom contains the linear effect across all categories; the second degree of freedom, the quadratic effect; and so on. These contrasts are often used to estimate polynomial trends.

Custom
The average group means in partition 2 are compared to the average group means in partition 1. Toggle the Show coefficients control to display or change the coefficient values next to each partition group. You can use the drop-down lists to change the groups is each partition, and click Add group to include more groups (when available).


Reference

https://www.ibm.com/docs/en/spss-statistics/beta?topic=fac-define-contrast

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