Since Richard Freeman wrote labour economics for the first (1987) edition of The New Palgrave: A Dictionary of Economics, labour economics has become increasingly empirical, with less emphasis on theory. The most noticeable change in empirical work is an increased emphasis on the plausibility of identification assumptions such as the validity of instrumental variables. Among the areas growing or receiving the greatest attention are changes in the wage structure, the economics of education, social interactions and personnel economics. The range of topics studied by labour economists today has broadened far beyond those of traditional labour economics.