Response variances, var(yi), are estimated using replications for each experimental condition. The resulting estimated variances can be used to derive the correct variances of the Ordinary A 2 Least Squares (OLS) estimators β. The estimates si can also be used to compute the Estimated Weighted Least Squares (EWLS) estimators β*. The asymptotic covariance formula for EWLS might be utilized to test the EWLS estimators. The type I and type I1 errors of this test procedure are compared to the corresponding A errors for the OLS estimators β.