Comparing Fixed Effects and Covariance Structure Estimators

Abstract

In this paper we compare the traditional econometric fixed effect/first difference estimator with the maximum likelihood estimator implied by covariance structure models for panel data. Our findings are that the maximum likelihood estimator is remarkable robust to mis-specifications, however in general the fixed estimator is preferable in small samples. Furthermore, we argue that we can use the Hausman test as a test of consistency of the maximum likelihood estimator. Finally we show that the covariance structure models is not identified in the case of time-invariant independent variables.