Using data on three million U.S. patents granted between 1967 and 1999, and their citations received between 1975 and 2002, the authors construct a number of measures of general purpose technolgies, including generality, number of citations, and patent class growth, for patents themselves and for the patents that cite the patents.
Link
http://emlab.berkeley.edu/users/bhhall/papers/HallTrajtenberg04_GPT.pdf