SPSS® 12.0 Command Syntax Reference

476 DISCRIMINANT
• When multiple FUNCTIONS subcommands are specified, the program uses the last;
however, if n 2 or n 3 are omitted on the last FUNCTIONS subcommand, the corresponding
specifications on the previous FUNCTIONS subcommands will remain in effect.
Example
DISCRIMINANT GROUPS=CLASS(1,5)
/VARIABLES = SCORE1 TO SCORE20
/FUNCTIONS=4,100,.80.
• The first two parameters on the FUNCTIONS subcommand are defaults: the default for n1 is 4 (the number of groups minus 1), and the default for n2 is 100.
• The third parameter tells DISCRIMINANT to use fewer than four discriminant functions if
the significance level of a function is greater than 0.80.
PRIORS Subcommand
By default, DISCRIMINANT assumes equal prior probabilities for groups when classifying
cases. You can provide different prior probabilities with the PRIORS subcommand.
• Prior probabilities are used only during classification.
• If you provide unequal prior probabilities, DISCRIMINANT adjusts the classification
coefficients to reflect this.
• If adjacent groups have the same prior probability, you can use the notation n*c on the
value list to indicate that n adjacent groups have the same prior probability c.
• You can specify a prior probability of 0. No cases are classified into such a group.
• If the sum of the prior probabilities is not 1, the program rescales the probabilities to sum
to 1 and issues a warning.
EQUAL Equal prior probabilities. This is the default.
SIZE Proportion of the cases analyzed that fall into each group. If 50% of the
cases included in the analysis fall into the first group, 25% in the second, and
25% in the third, the prior probabilities are 0.5, 0.25, and 0.25, respectively.
Group size is determined after cases with missing values for the predictor variables
are deleted.
Value list User-specified prior probabilities. The list of probabilities must sum to 1.0.
The number of prior probabilities named or implied must equal the number
of groups.
Example
DISCRIMINANT GROUPS=TYPE(1,5)
/VARIABLES=A TO H
/PRIORS = 4*.15,.4.
• The PRIORS subcommand establishes prior probabilities of 0.15 for the first four groups
and 0.4 for the fifth group.