Modeling and Multivariate Methods - SAS

Chapter 9 Performing Nonlinear Regression 245
Example of Nonlinear Fitting
Notice that the Inflection Point parameter for the test B formulation is significantly lower than the average
inflection point. This agrees with what we noticed in the plots of the fitted models.
Launch the Nonlinear Platform
To launch the Nonlinear platform, select Analyze > Modeling > Nonlinear. The launch window is shown
in Figure 9.4.
Figure 9.4 Nonlinear Launch Window
Begin fitting a nonlinear model in one of two ways:
• Provide the Y and X variables and fit one of the built-in nonlinear models. This launches the Fit Curve
personality of the Nonlinear platform. See “Nonlinear Fitting with Fit Curve” on page 246.
• If you want to fit a model that is not in Fit Curve, you must first create a formula column that defines
the model. This formula must include parameters to be estimated and the initial values of the
parameters. Any nonlinear model can be fit using this method. For more information about this process,
see “Fit a Custom Model” on page 256.
You can also create the formula column using the Model Library. The Model Library creates the formula
column and parameters, and helps you choose initial values, but only for models that are in Model
Library. See “Use the Model Library” on page 264.