Basic Analysis and Graphing - SAS

Chapter 4 Performing Bivariate Analysis 107
Fit Spline
Figure 4.14 Example of Fit Special Flowchart
Transformation?
Yes
No
Transformed
Fit Report
and menu
Degree?
1 2-5
Linear Fit
Report and
menu
Polynomial
Fit Report
and menu
Transformed Fit Report
The Transformed Fit report contains the reports described in “Linear Fit and Polynomial Fit Reports” on
page 99.
However, if you transformed Y, the Fit Measured on Original Scale report appears. This shows the measures
of fit based on the original Y variables, and the fitted model transformed back to the original scale.
Related Information
• “Example of the Fit Special Command” on page 118
• “Linear Fit and Polynomial Fit Reports” on page 99
• “Fitting Menus” on page 115
Fit Spline
Using the Fit Spline command, you can fit a smoothing spline that varies in smoothness (or flexibility)
according to the lambda (λ) value. The lambda value is a tuning parameter in the spline formula. As the
value of λ decreases, the error term of the spline model has more weight and the fit becomes more flexible
and curved. As the value of λ increases, the fit becomes stiff (less curved), approaching a straight line.
Note the following information:
• The smoothing spline can help you see the expected value of the distribution of Y across X.
• The points closest to each piece of the fitted curve have the most influence on it. The influence increases
as you lower the value of λ, producing a highly flexible curve.