Student test is frequently used in order to determine the significance of estimated parameters of linear
regressions. But, in many cases, the Student test statistics of multiple linear regressions are sensibly different
from the statistics obtained for the analyzed explanatory variables in case of simple linear regressions. The
main cause of the respective differentiation is due to the collinearity, in other words because of departure from
orthogonality between the explanatory variables (Glauber, Farrar, 1967). But if we consider some indicators
such as Variance of Inflation Factor or coefficients of collinear refraction, we are able to explain the correlation
between the Student statistics obtained in case of simple and multiple linear regressions.