Basic Analysis and Graphing - SAS

106 Performing Bivariate Analysis Chapter 4
Fit Special
Related Information
• “Statistical Details for Fit Line” on page 124
• “Fitting Menus” on page 115
Fit Special
Using the Fit Special command, you can transform Y and X. Transformations include the following: log,
square root, square, reciprocal, and exponential. You can also constrain the slope and intercept, fit a
polynomial of specific degree, and center the polynomial.
Table 4.8 Description of the Specify Transformation or Constraint Window
Y Transformation
X Transformation
Degree
Centered Polynomial
Constrain Intercept to
Constrain Slope to
Use these options to transform the Y variable.
Use these options to transform the X variable.
Use this option to fit a polynomial of the specified degree.
To turn off polynomial centering, deselect the Centered Polynomial check
box. See Figure 4.20. Note that for transformations of the X variable,
polynomial centering is not performed. Centering polynomials stabilizes
the regression coefficients and reduces multicollinearity.
Select this check box to constrain the model intercept to be the specified
value.
Select this check box to constrain the model slope to be the specified value.
Fit Special Reports and Menus
Depending on your selections in the Fit Special window, you see different reports and menus. The flowchart
in Figure 4.14 shows you what reports and menus you see depending on your choices.