Hausman (1978) developed a widely-used model specification test that has passed the test of time. In this paper, we show that the asymptotic variance of the difference of the two estimators can be a singular matrix. Three illustrative examples are used, namely an exogeneity test for the linear...

Adopting both linear and nonlinear Granger causality tests, we find consumer attitude indices of the University of Michigan's surveys are very useful in predicting consumption movements of the United States.