1. Brockhaus Enzyklopädie, 1990. Brockhaus, Mannheim, Germany.
2. Censimento Generale della Popolazione Generale, 1991. Istituto Nazionale di Statistica, ISTAT, Rome, Italy.
3. Productivity and the density of economic activity;Ciccone;American Economic Review,1996
4. Ciccone, 1997. Technology diffusion, dynamic externalities, and the spatial distribution of wages in the US. Mimeo. University of California, Berkeley.
5. Encyclopedia Italiana, 1935. Rizzoli, Milan, Italy.