Most tests for heteroskedasticity take this basic form. The main differences between popular tests are which transformations of enter Motivated by the form of the asymptotic variance of the OLS estimator White (1980) proposed that the test for heteroskedasticity be based on setting to equal all non-redundant elements of , its squares, and all cross-products. Breusch-Pagan (1979) proposed what might appear to be a distinct test, but the only difference is that they allowed for general choice of , and replaced with which holds when is If this simplification is replaced by the standard formula (under independence of the error), the two tests coincide.
It is important not to misuse tests for heteroskedasticity. It should not be used to determine whether to estimate a regression equation by OLS or FGLS, nor to determine whether classic or White standard errors should be reported. Hypothesis tests are not designed for these purposes. Rather, tests for heteroskedasticity should be used to answer the scientific question of whether or not the conditional variance is a function of the regressors. If this question is not of economic interest, then there is no value in conducting a test for heteorskedasticity