http://web.missouri.edu/~kolenikovs/Stat9370/democindus.txt(link no longer valid; see discussion on SEMNET 18 Jun 2009)
Bollen, K. A. (1979). Political democracy and the timing of development. American Sociological Review, 44, 572-587.
Bollen, K. A. (1980). Issues in the comparative measurement of political democracy. American Sociological Review, 45, 370-390.