Worked example. The influence function for robust fitting, prior to the first iteration. The influence function is defined as RR/(1+RR2), where RR is defined in Equation 13. Even the points with the largest residuals (to the right on the graph) have substantial influence.
Motulsky and Brown BMC Bioinformatics 2006 7:123 doi:10.1186/1471-2105-7-123