Workspace Node: Boosted Classification Trees - Specifications - Classification Tab
In the Boosted Classification Trees workspace node dialog box, under the Specifications heading, select the Classification tab to access the following options.
| Element Name | Description |
|---|---|
| Misclassification costs | Use the options in this group box to assign greater importance to the accurate prediction (classification) for some classes as compared to others. For example, in medical research you may want assign greater importance to the accurate classification of malignant tumors, compared to accurate discrimination between different types of benign forms. In this case, you would assign greater costs to the misclassification of malignant tumors, and lower costs to the misclassification of benign tumors. Note also that, as illustrated in this example, the matrix of misclassification costs does not necessarily have to be symmetric, and in fact it rarely is (i.e., it is more costly to misclassify malignant tumors as benign, than the other way around).
The misclassification costs are combined with the prior probabilities when computing the classification probabilities (during estimation, as well as when computing the final classification probabilities); for details regarding these computations, see Friedman (1999a, p. 11; essentially, the cost will be applied as a relative weight to the classification probabilities, and final classifications will be determined from the products of the two). |
| Equal | When you select this option button, each off-diagonal element of the predicted class (row) by observed class (column) misclassification costs matrix is set equal to 1.0, and the specified prior probabilities for the classes on the dependent variable are not adjusted. |
| User specified | Select this option button if more accurate classification is desired for some classes than others. Note that this option is available only if you have selected the dependent variable codes by clicking the Response codes button on the Specifications - Quick tab. |
| Prior probabilities | Use the options in this group box to specify how likely it is, without using any prior knowledge of the values for the predictor variables in the model, that a case or object will fall into one of the classes. Note that the
User specified option is available only after you have selected the specific
Response codes for the dependent variable on the
Specifications - Quick tab.
The prior probabilities will be combined with the prediction probabilities and misclassification costs to compute the classification probabilities during the estimation (building of trees), and to compute the final classifications (see also, Computational Details). |
| Estimated | Select this option button to specify that the likelihood that a case or object will fall into one of the classes is proportional to the dependent variable class sizes. |
| Equal | Select this option button to specify that the likelihood that a case or object will fall into one of the classes is the same for all dependent variable classes. |
| User specified | Select this option button if you have specific knowledge about the base rates (for example, based on previous research). When you click the adjacent button, the Enter values for the prior probabilities dialog box is displayed, where you can specify the
a priori probabilities for each class of the dependent variable. If the probabilities do not add up to 1.0, Statistica will automatically adjust them proportionately.
Options / C / W. See Common Options. |
| OK | Click this button to accept all the specifications made in the dialog box and to close it. The analysis results are placed in the Reporting Documents workspace node after running (updating) the project. |