# Minitab Help 9: Influential Points

### Influence 1 (no influential points)

### Influence 2 (outlier, low leverage, not influential)

- Create a basic scatterplot.
- Perform a linear regression analysis for all the data (click "Storage" in the regression dialog and select "Fits" to save the fitted values).
- Select Data > Subset Worksheet to create a worksheet that excludes observation #21 and Perform a linear regression analysis.
- Return to the original worksheet and select Calc > Calculator to calculate fitted values based on the fitted equation for the subsetted worksheet, e.g., FITX = 1.73+5.117*x.
- Return to the scatterplot and select Editor > Calc > Calculated Line with y=FITS and x=x to add a regression line to the scatterplot.
- Select Editor > Calc > Calculated Line with y=FITX and x=x to add a regression line based on the fitted equation for the subsetted worksheet.
- Click "Storage" in the regression dialog to calculate leverages, standardized residuals, studentized (deleted) residuals, DFFITS, Cook's distances.

### Influence 3 (high leverage, not an outlier, not influential)

- Create a basic scatterplot.
- Perform a linear regression analysis for all the data (click "Storage" in the regression dialog and select "Fits" to save the fitted values).
- Select Data > Subset Worksheet to create a worksheet that excludes observation #21 and Perform a linear regression analysis.
- Return to the original worksheet and select Calc > Calculator to calculate fitted values based on the fitted equation for the subsetted worksheet, e.g., FITX = 1.73+5.117*x.
- Return to the scatterplot and select Editor > Calc > Calculated Line with y=FITS and x=x to add a regression line to the scatterplot.
- Select Editor > Calc > Calculated Line with y=FITX and x=x to add a regression line based on the fitted equation for the subsetted worksheet.
- Click "Storage" in the regression dialog to calculate leverages, DFFITS, Cook's distances.

### Influence 4 (outlier, high leverage, influential)

- Create a basic scatterplot.
- Perform a linear regression analysis for all the data (click "Storage" in the regression dialog and select "Fits" to save the fitted values).
- Select Data > Subset Worksheet to create a worksheet that excludes observation #21 and Perform a linear regression analysis.
- Return to the original worksheet and select Calc > Calculator to calculate fitted values based on the fitted equation for the subsetted worksheet, e.g., FITX = 1.73+5.117*x.
- Return to the scatterplot and select Editor > Calc > Calculated Line with y=FITS and x=x to add a regression line to the scatterplot.
- Select Editor > Calc > Calculated Line with y=FITX and x=x to add a regression line based on the fitted equation for the subsetted worksheet.
- Click "Storage" in the regression dialog to calculate leverages, DFFITS, Cook's distances.

### Foot length and height (outlier, high leverage, influential)

- Create a basic scatterplot.
- Perform a linear regression analysis for all the data. Click "Storage" in the regression dialog to calculate DFFITS, Cook's distances.
- Select Data > Subset Worksheet to create a worksheet that excludes observation #28 and Perform a linear regression analysis.

### Hospital infection risk (two outliers, high leverages)

- Perform a linear regression analysis for all the data.
- Create a fitted line plot.