CHAID is the name of an algorithm for creating decision trees, which uses chi-square tests (this is what the CH in CHAID refers to).
Although Q does not have CHAID, this is only because it uses a more modern approach which takes advantage of advances in computing and statistics since CHAID was developed. See Trees for a description of the approach used in Q and The difference between Trees, CHAID, CART and other tree-based models for a description of the difference between Q's approach, CHAID and related algorithms.
In Q you can use the CHAID algorithm to automatically combine categories in categorical variables. For this, please refer to:
- Create New Variables - Automatically Combine Categories - By Pattern (CHAID) - Any Categories
- Create New Variables - Automatically Combine Categories - By Pattern (CHAID) - Adjacent Categories
Further reading: Market Segmentation Software
- * Kass, Gordon V.; An Exploratory Technique for Investigating Large Quantities of Categorical Data, Applied Statistics, Vol. 29, No. 2 (1980), pp. 119–127