Another suggested rule is to consider any value greater than 1 or 2 as indicating that an observation requires a careful look. Finally, some researchers look for gaps between the D values. In summary, Cook's D assesses the global impact of each observation on the parameter estimates and, equivalently, on the predictions for all other observations. Large values of D identify those observations with large impacts. We therefore can use Cook's D to answer this third question.
Large values correspond to points which have a big influence on the fitted model.
The Statlet's application does calculate Cook's D values as shown in the Output tab below. You can then report a good model for those observations which you do understand. By clicking the Predicted Plot tab, Statlets produces a very valuable plot for evaluating outliers. The plot displays the observed values of the criterion variable versus the regression solution. This plot displays observed values of SAT versus values predicted by the fitted model.