This function combines a number of criteria for determining whether a
datapoint is an influential case in a regression analysis. It then sum the
criteria to compute an index of influentiality. A list of cases with an
index of influentiality of 1 or more is then displayed, after which the
regression analysis is repeated without those influantial cases. A
scattermatrix is also displayed, showing the density curves of each
variable, and in the scattermatrix, points that are colored depending on how
influential each case is.