Creating Alternative Models to Compare

Once you have fitted and examined a single model (either one- or two-stage), you will normally want to create more models to search for the best fit. You can:

• Create individual new models.

  • You can create new child nodes by clicking the New button from any modeling node. The Model Setup dialog box appears where you can change the type and settings. You can repeat this for multiple child nodes to create a selection of different model types fitted to the same data.

• Create a template to save a variety of model settings for reuse.

  • From any global or one-stage model with child nodes, select Model > Make Template. You can save the child node model types of your currently selected modeling node as a template. You can then use the Build Models dialog box to find your user-defined templates and quickly build all those model types again for any global model you choose (see below).

  • From any global model node (before calculating MLE), click Build Models in the toolbar. You can save a template containing whatever models you choose by selecting New and adding the model types you want.

• Use the Build Models function to create a selection of models at once. You can create templates, use predefined templates, and use models in the current project as a template. All the child node model types in the template you select are built as child nodes of the currently selected global model. See Boundary Model Setup.

Creating a template containing a list of all the models you want is a very efficient way to quickly build a selection of alternative model child nodes for many global models. Use these techniques to find models that fit well to the data for each of your global models.

We provide a detailed tutorial example to guide you through using these techniques to make a number of models to compare. See the modeling tutorial section Creating Multiple Models to Compare in the Getting Started documentation. This tutorial section requires you to have completed the previous steps in the Quick Start tutorial, so that you have an initial model as a starting point.

Note that you can click New from any modeling node to create new child nodes.

• For all global model nodes (one- and two-stage) a new child node appears that is a copy of the parent, and the Model Setup dialog box appears where you can change the type and settings.

• For the other two-stage modeling nodes (local and response models) you also get a new child node but the procedure is slightly different — see the tutorial example for details.

Once you have a variety of models to compare, you should use the diagnostic statistics and powerful visual aid plotting capabilities of the Model Browser to help you decide which models are best. For a description of the views and statistics available in each modeling view, see:

• Selecting Models

• Model Evaluation Window

• Local Models

• Global Models

• Response Level

For linear models, make use of the Stepwise functions (open the Stepwise window for existing models, and/or choose a Stepwise option during model setup) to refine your models and remove less useful model terms. Make sure you examine outliers but do not automatically remove them without good reason. Pay attention to the diagnostic statistics to help you find the best models. The following sections describe how to use Stepwise to make better models and how to understand the diagnostic statistics:

• Model Selection Guide for guidelines.

• Stepwise for an introduction to Stepwise.

• PRESS statistic — See this section for guidelines on what to look for in the statistics to indicate a good fit.

How to Set Up a Point-by-Point Model

Projects and Test Plans

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