Specify the default settings for regression trees

File > Options > Predictive Analytics > CART® Regression

Specify the default methods for regression trees. The changes you make to the defaults remain until you change them again, even after you exit Minitab.

Node splitting method
Choose the splitting method to generate your decision tree. You can compare the results from both splitting methods to determine the best choice for your application.
  • Least squared error: The least squared error method is the default method that works well across many applications. The least squared error method minimizes the sum of the squared errors.
  • Least absolute deviation: The least absolute deviation method minimizes the sum of absolute values of errors.
Criterion for selecting optimal tree
When Least squared error is the criterion for the node splitting method, choose between these criteria to produce the tree in the results. You can compare results from different trees to determine the best choice for your application.
Maximum R-squared
Select this option to display results for the tree with the maximum R-squared value.
Within K standard errors of maximum R-squared; K=
Select this option to have Minitab choose the smallest tree with an R2 value that falls within K standard errors of the tree with the maximum R2 value. By default, K=1, so the tree in the results is the smallest classification tree with an R2 value within 1 standard error of the maximum R2 value.
When Least absolute deviation is selected as the node splitting method, choose between these criteria to select the tree in the results. You can compare the results from different trees to determine the best choice for your application.
Least mean absolute deviation
Select this option to display results for the tree with the least mean absolute deviation.
Within K standard errors of least mean absolute deviation; K=
Select this option to have Minitab choose a tree with a mean absolute deviation value that falls within K standard errors of the tree with the least mean absolute deviation value. By default, K=1, so the tree in the results is the smallest classication tree with a mean absolute deviation value within 1 standard error of the minimum least absolute deviation value.
Minimum number of cases to split an internal node
Enter a value to represent the minimum number of cases an internal node to be split. The default is 10. With larger sample sizes, you may want to increase this minimum. For example, if an internal node has 10 or more cases, Minitab will try to perform a split. If the internal node has 9 cases or less, Minitab will not try to perform a split.
The internal node limit must be at least twice the terminal node limit, but larger ratios are better. Internal node limits of at least 3 times terminal node limits allow a reasonable number of splitters.
The default value is 10.
Minimum number of cases allowed for a terminal node
Enter a value to represent the minimum number of cases that may be separated into a terminal node. The default is 3. With larger sample sizes, you may want to increase this minimum. For example, if a split would create a node with less than 3 cases, Minitab will not perform a split.
The default value is 3.
Missing value penalty
Enter a penalty value for a predictor with missing values. Because it is easier to be a good splitter with less data, predictors with missing data have an advantage over predictors without missing data. Use this option to penalize predictors with missing data.
0.0 ≤ K ≤ 2.0, for example:
  • K = 0: Specifies no penalty.
  • K = 2: Specifies highest penalty.
High level category penalty
Enter a penalty value for categorical predictors that have many values. Because categorical predictors with many levels can distort a tree due to their increased splitting power, they have an advantage over predictors with less levels. Use this option to penalize predictors with many levels.
0.0 ≤ K ≤ 5.0, for example:
  • K = 0: Specifies no penalty.
  • K = 5: Specifies highest penalty.
Display of graphs and tables
Residuals for plots
Specify the type of residuals to display on the boxplot of residual plots.
  • Regular: By default, the boxplot displays regular residuals.
  • Percent: Specify to display the percentage residuals on the boxplot.
Terminal node type
Choose whether to display the best nodes, the worst nodes, or both for the Fits and error statistics table and the Criteria for classifying subjects table.
  • Best: By default, Minitab displays the best terminal nodes. The best nodes have the lowest MSE or MAD values.
  • Worst: Select to display the worst terminal nodes. The worst nodes have the highest MSE or MAD values.
  • Best and Worst: Select to display the best and the worst terminal nodes.
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