Deviation

Deviation from the grand mean. In matrix terms, these contrasts have the form:

   mean (  1/k    1/k   ...   1/k   1/k)
  df(1) (1-1/k   -1/k   ...  -1/k  -1/k)
  df(2) ( -1/k  1-1/k   ...  -1/k  -1/k)
      .             .
      .             .
df(k-1) ( -1/k   -1/k   ... 1-1/k  -1/k)

where k is the number of categories for the independent variable and the last category is omitted by default. For example, the deviation contrasts for an independent variable with three categories are as follows:

( 1/3   1/3   1/3)
( 2/3  -1/3  -1/3)
(-1/3   2/3  -1/3)

To omit a category other than the last, specify the number of the omitted category in parentheses after the DEVIATION keyword. For example, the following subcommand obtains the deviations for the first and third categories and omits the second:

/CONTRAST(FACTOR)=DEVIATION(2)

Suppose that factor has three categories. The resulting contrast matrix will be

( 1/3   1/3   1/3)
( 2/3  -1/3  -1/3)
(-1/3  -1/3   2/3)