Ana Rute Cardoso, "Wage Differentials across Firms: An Application of Multilevel Modelling", Journal of Applied Econometrics, Vol. 15. No. 4, 2000, pp. 343-354. The data used are gathered by the Department of Statistics, Ministry of Employment and Solidarity of Portugal. "Quadros de Pessoal" is a matched dataset of firms, plants and their workers, covering every plant with wage-earners in the Portuguese economy, with the exception of agriculture and civil servants. The original dataset covers around two million workers each year. Reported data include the worker's gender, age, skill, occupation, schooling, tenure, earnings, and duration of work, as well as the mechanism of wage bargaining, the establishment's location, industry and employment, and the firm's location, industry, employment, sales, legal setting, shares of private, public and foreign capital and date of creation. Most concepts used meet international standards. For confidentiality reasons, the Ministry of Employment and Solidarity does not permit open access to the data. Data requests should be directed to Ministry of Employment and Solidarity Department of Statistics Rua Rodrigo da Fonseca, 55 1250 Lisboa Portugal Further details on the dataset can be provided by: Ana Rute Cardoso University of Minho NIMA Gualtar, 4710-057 Braga, Portugal cardoso@eeg.uminho.pt