Building the flow (SPSS Modeler)

Building the flow

Once the Introduction to Modeling flow loads, you can see that part of the SPSS Modeler flow is already set up.

To build a flow and create a model, you need at least three nodes: a Data Asset node, a Type node, and a modeling node. Optionally, you can also add Table or Analysis nodes.

Data Asset node

This node reads data from an external source, in this case the tree_credit.csv data file. If you specify measurements in the source node, you don’t need to include a separate Type node in the flow.

Type node

This node specifies field properties, such as measurement level (the type of data that the field contains), and the role of each field as a target or input in modeling. The measurement level is a category that indicates the type of data in the field. The source data file uses three different measurement levels:

A Continuous field (such as the Age field) contains continuous numeric values.
A Nominal field (such as the Education field) has two or more distinct values—in this case College or High school.
An Ordinal field (such as the Income level field) describes data with multiple distinct values that have an inherent order—in this case Low, Medium, and High.

Figure 2. Setting the target and input fields with the Type node

For each field, the Type node also specifies a role to indicate the part that each field plays in modeling. The role is set to Target for the field Credit rating, which is the field that indicates whether a customer defaulted on the loan. The target is the field for which you want to predict the value.

Role is set to Input for the other fields. Input fields are sometimes known as predictors, or fields whose values are used by the modeling algorithm to predict the value of the target field.

Modeling node

A modeling node generates a model nugget when the flow runs. This example uses a CHAID node. CHAID, or Chi-squared Automatic Interaction Detection, is a classification method that builds decision trees by using a particular type of statistics that are known as chi-square statistics. The node uses chi-square statistics to work out the best places to make the splits in the decision tree.

The CHAID modeling node generates the model. In the node's properties, under FIELDS, the option to Use custom field roles is available. You could select this option and change the field roles. However, in this example, use the default targets and inputs as specified in the Type node.

Table or Analysis nodes

These nodes are optional. You can connect a Table or Analysis node to the model nugget to view the scoring results after the model nugget is added to the flow.

The three main nodes are already connected. So, all you need to do is configure the CHAID node.

Double-click the CHAID node (named Creditrating). The node properties are displayed.
Figure 3. CHAID modeling node properties

The CHAID node has several options where you could specify the kind of model you want to build.

For this example, the goal is to create a brand-new model. Under OBJECTIVES use the default Build new model option.

To create a single, standard decision tree model without any enhancements, use the default objective option Create a standard model.

Figure 4. CHAID modeling node objectives

To keep the tree fairly simple for this example, limit the tree growth by raising the minimum number of cases for parent and child nodes.
Under STOPPING RULES, select Use absolute value.
Set Minimum records in parent branch to 400.
Set Minimum records in child branch to 200.

Figure 5. Setting the stopping criteria for decision tree building

You can use all the other default options for this example, so click Save and then click the Run on the toolbar to create the model. Alternatively, hover over the CHAID node, then click the overflow menu and select Run.