Minitab Help 11: Influential Points

Minitab 18

Minitab®

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)

Hospital infection risk (two outliers, high leverages)