18. Lotka, Alfred J. (1926). The frequency distribution of scientific productivity. Journal of the Washington Academy of Sciences 16 (12). 317-323. Disponible en http://listserv.utk.edu/cgi-bin/wa?A3=ind0709&L=sigmetrics&P=52661&E=2&B=--%3D-YUefx%2F0auEG8%2B29U7Cdc&N=Lotka+1929.pdf&T=application%2Fpdf