‎The method of least squares is a very simple‎, ‎practical and useful approach for estimating regression coefficients of the linear models‎. ‎This statistical method is used by users of different fields to provide the best unbiased linear estimator with the least variance‎. ‎Unfortunately‎, ‎this method will not have reliable output if outliers are present in the dataset‎, ‎as the collapse point (estimator consistency criterion) of this method is 0% ‎. ‎It is therefore important to identify these observations‎. Until now, ‎the various methods have been proposed to identify these observations‎. ‎In this article‎, the proposed methods are ‎reviewed ‎and ‎discussed in details‎‎‎. ‎Finally‎, ‎by presenting a simulation example‎, ‎we examine each of the proposed methods‎.