Two graphical displays for outlying and influential observations in regression

The paper describes two procedures for detecting observations with outlying values either in the response variable or in the explanatory variables in multiple regression. These procedures are presented as half normal plots with envelopes derived from simulation in order to avoid overinterpretation of the data. Analysis of a well-known data set leads to the use of a data transformation, a simple test for which is commended, and to some comments on the relationship with robust regression.