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Why does the tree change when non-splitting variables are dropped?

If a variable does not enter the tree as a primary node splitter, it may still play a important role in the tree as a surrogate splitter. If you have turned the displaying of surrogate splitters off, you will not see how these variables affect the tree but they will still be used internally by CART when applying the tree to data. The Variable Importance Table produced by CART ranks the variables in the tree by their importance, a statistic measuring how strongly a variable acts as a primary or surrogate splitter.

Working With A Large Number of Variables In SPM®

Salford Systems Predictive Modeler, including CART®, MARS®, TreeNet®, and RandomForests®, can handle any number of variables you care to work with. By default your software will launch prepared to work with up to 32,768 variables which is sufficient for many users. However, if you need to work with a larger number you just need to let the software know at the time the application is launched.

Working With Date Variables

There are a variety of ways to represent dates in data files and there is standard, which can make life difficult if one is trying to use date variables in a predictive model. Two of the more common representations are the Microsoft date format (used in Excel and other Microsoft products) , which is the number of days since December 30, 1899; and the SAS date format, which is the number of days since January 1, 1960. For the sake of establishing consistency, the data access library used by SPM® converts all date variables to Microsoft dates. The advantage of doing so is that one does not have to guess how dates are represented in the input dataset and Microsoft products are common; the disadvantage is that you might be confused if you are using non-Microsoft products (like SAS) to manage your data.

Working with Scratch Directories in SPM®

Like many programs, the Salford Predictive Modeler® software suite reads, writes, and otherwise manages temporary files in the course of its work. These are written to a particular directory on your computer called a "scratch directory". SPM also writes a command log to the scratch directory. The GUI version of SPM allows the location of this directory to be set as an option (with a sensible default), but non-GUI versions determine where to write temporary files by means of environment variables. Presently, SPM searches for the following environment variables and uses the value of the first one defined as its scratch directory:

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