# Fitting a Quadratic in JMP®

## Chapter 4, Printout 2

### Section 1: Making a Fitted Quadratic Plot

1. Launch JMP and create a new data table.

2. Enter the data.

• Rename Column 1 to "x" and enter the Ammonium Phosphate data from the x column in Table 4.3 (p. 133).

• Add a second column, "y," and enter the Compressive Strength data from the table.
Screenshot:

3. Generate a fitted quadratic plot of the data.

• Select "Analyze --> Fit Y by X."

• In the dialog box that follows, click "y" in the list labeled "Select Columns"; then click "Y, Response" to designate y as the response variable.

• Click "x," then "X, Factor" to designate x as the factor variable.

Screenshot:

• Click "OK."

JMP displays a scatter plot of y vs. x.

Screenshot:

• Click the red triangle next to the label, "Bivariate Fit of Density By Pressure." Select "Fit Polynomial --> 2,quadratic" from the resulting pop-up menu.

JMP fits a quadratic to the points, plots the quadratic, and displays an analysis of the fit.

Screenshot:

### Section 2: Obtaining Additional Numerical Summaries

1. Save predicted y values for the x values given in the table.

• Beneath the plot generated in Section 1, click the red triangle next to the label, "Polynomial Fit Degree=2."

• Select "Save Predicteds" from the pop-up menu.

JMP saves the predicted y values to a new column in the data table.

Screenshot:

2. Save the residuals.

• Beneath the plot, click the red triangle next to the label, "Polynomial Fit Degree=2."

• Select "Save Residuals" from the pop-up menu.

JMP saves the y residuals to a new column in the data table.

Screenshot:

### Section 3: Generating Additional Plots

1. Plot Residuals vs. x.

• Beneath the plot generated in Section 1, click the red triangle next to the label, "Polynomial Fit Degree=2."

• Select "Plot Residuals" from the pop-up menu.

JMP plots residuals vs. x and appends the plot to the current window.

Screenshot:

2. Generate a Normal Plot of the Residuals.

• Select "Analyze --> Distribution."

• In the dialog box that follows, click "Residuals y" in the list labeled "Select Columns"; then click "Y, Columns" to add the residuals column to the list of columns to be analyzed.

Screenshot:

• Click "OK."

JMP displays the distribution of the residuals.

Screenshot:

• Click the red triangle next to the label, "Residuals y."

• Select "Display Options --> Horizontal Layout."

JMP changes the layout of the window and the orientation of the plot.

Screenshot:

• Click the red triangle next to the label, "Residuals y."

• Select "Normal Quantile Plot" from the pop-up menu.

JMP generates a normal plot and displays it in the current window.

Screenshot: