Estimating wage differentials without logarithms

Regression models of wage determination are typically estimated by ordinary least squares using the logarithm of the wage as the dependent variable. These models provide consistent estimates of the proportional impact of wage determinants only under the assumption that the distribution of the error term is independent of the regressors - an assumption that can be violated by the presence of heteroskedasticity, for example. Failure of this assumption is particularly relevant in the estimation of the impact of union status on wages. Alternative wage-equation estimators based on the use of quasi-maximum-likelihood methods are consistent under weaker assumptions about the dependence between the error term and the regressors. They also provide the ability to check the specification of the underlying wage model. Applying this approach to a standard data set, I find that the impact of unions on wages is overstated by a magnitude of 20-30 percent when estimates from log-wage regressions are used for inference. (c) 2005 Elsevier B.V. All rights reserved.