Data Smoothing: Polynomial Regression

The Plots Tab

You can use the Plots tab (Figure 20.4) to create plots that graphically display results of the analysis. The raw residuals are computed as , where indicates the variable containing the predicted values of the response.

Creating a plot often adds one or more variables to the data table. The following plots are available:

Observed vs. Explanatory with smoother

creates a scatter plot of the X and Y variables, overlaid with the polynomial smoother.

Confidence limits for means

specifies whether to add 95% upper and lower confidence limits to the Observed vs. Explanatory plot.

Prediction limits for individuals

specifies whether to add 95% upper and lower individual prediction limits to the Observed vs. Explanatory plot.

Observed vs. Predicted

creates a scatter plot of the Y variable versus the predicted values.

Raw residuals vs. Predicted

creates a scatter plot of the residuals versus the predicted values.

Raw residuals vs. Explanatory

creates a scatter plot of the residuals versus the X variable.

Residual normal QQ

creates a normal Q-Q plot of the residuals.

Note: Stat Studio adds a smoother to an existing scatter plot when both of the following conditions are satisfied:

• The scatter plot is the active window when you select the analysis.
• The scatter plot variables match the analysis variables.

Chapter 18, "Data Smoothing: Loess," discusses how to display multiple smoothers in a single scatter plot, and how to remove smoothers from a scatter plot.