Intervals
The Intervals dialog box is displayed when you select to modify the (current or default) intervals for continuous predictors for CHAID and Exhaustive CHAID analyses by clicking the Intervals button on the Interactive Trees Specifications dialog box - Advanced tab. With the Interactive Trees (C&RT, CHAID) module, you have full control over the manner in which the range of values in continuous predictors in CHAID and Exhaustive CHAID analyses is divided into intervals (unlike the General CHAID Models module, which applies automatic algorithms for building trees; see Basic Tree-Building Algorithm: CHAID and Exhaustive CHAID for details; see also the Introductory Overview topic, Differences in Computational Procedures section).
Use the options in this dialog box to specify how exactly the range of values in the selected continuous predictor variable is to be divided into intervals.
| Element Name | Description |
|---|---|
| OK | Click this button to accept the current intervals for the current continuous predictor variable. |
| Cancel | Click Cancel to abandon the current specifications and revert to the intervals for the current continuous predictor as they existed prior to displaying this dialog box. |
| Remove all | Click Remove all to remove all intervals except the first interval. As a result, only a single interval will be defined, which you can further modify or augment. |
| Remove | Click Remove to delete the currently highlighted interval in the list of intervals. As a result, the cases in the interval that was removed will automatically be combined with the next interval (i.e., the next interval boundary "above" the deleted interval boundary will now apply to those case). |
| Intervals (Start/End/Cases/Percent) | The values shown in the spreadsheet define the intervals currently in effect, i.e., for each interval, the spreadsheet shows the lower interval boundary (Start), upper interval boundary (End), the number of cases in the respective interval (Cases), and the percent of cases in the respective interval (Percent). |
| Start of new interval/Add new interval | To add a new interval, first enter a (new) lower interval boundary into the Start of new interval box, and then click the Add new interval button. |
| Number of intervals/Update intervals | To automatically divide the range of values for the current continuous predictor variable into a fixed number of intervals, first specify the desired Number of intervals, and then click on the Update intervals button. Note that this operation will automatically update all intervals, and hence delete any "custom-intervals" that have previously been specified. |