According to Gauss-Markov theorem therefore, given the assumptions of the classical linear regre ssion model, the least squares estimators in the class of all linear
unbiased estimators, have minimum variance (i.e. BLUE) (Gujarati 2003, p. 79).
Given that the satisfaction of the assumptions of the classical linear regression is a
necessary condition for achieving BLUE, it is therefore worthwhile to test for the satisfaction of those assumptions because of the following reasons: