Discriminant Analysis Classification
Prior Probabilities. This option determines whether the classification coefficients are adjusted for a priori knowledge of group membership.
- All groups equal. Equal prior probabilities are assumed for all groups; this has no effect on the coefficients.
- Compute from group sizes. The observed group sizes in your sample determine the prior probabilities of group membership. For example, if 50% of the observations included in the analysis fall into the first group, 25% in the second, and 25% in the third, the classification coefficients are adjusted to increase the likelihood of membership in the first group relative to the other two.
Display. Available display options are casewise results, summary table, and leave-one-out classification.
- Casewise results. Codes for actual group, predicted group, posterior probabilities, and discriminant scores are displayed for each case.
- Summary table. The number of cases correctly and incorrectly assigned to each of the groups based on the discriminant analysis. Sometimes called the "Confusion Matrix."
- Leave-one-out classification. Each case in the analysis is classified by the functions derived from all cases other than that case. It is also known as the "U-method."
Replace missing values with mean. Select this option to substitute the mean of an independent variable for a missing value during the classification phase only.
Use Covariance Matrix. You can choose to classify cases using a within-groups covariance matrix or a separate-groups covariance matrix.
- Within-groups. The pooled within-groups covariance matrix is used to classify cases.
- Separate-groups. Separate-groups covariance matrices are used for classification. Because classification is based on the discriminant functions (not based on the original variables), this option is not always equivalent to quadratic discrimination.
Plots. Available plot options are combined-groups, separate-groups, and territorial map.
- Combined-groups. Creates an all-groups scatterplot of the first two discriminant function values. If there is only one function, a histogram is displayed instead.
- Separate-groups. Creates separate-group scatterplots of the first two discriminant function values. If there is only one function, histograms are displayed instead.
- Territorial map. A plot of the boundaries used to classify cases into groups based on function values. The numbers correspond to groups into which cases are classified. The mean for each group is indicated by an asterisk within its boundaries. The map is not displayed if there is only one discriminant function.
Choosing Classification Options
This feature requires the Statistics Base option.
- From the menus choose:
- In the Discriminant Analysis dialog box, click Classify.