Changes

The vast majority of papers use the GIM index or some variation that is created as a subset of the items in the original GIM index. Each index is constructed using the Investor Responsibility Research Center data from ''Corporate Takeover Defenses'' Rosenbaum 1990, 1993, 1995, 1998, 2000, 2002. I can only locate physical copies of these books, so I assume research assistants put together databases by hand using those physical copies.

In order to obtain this data, I would contact the authors of one of the more recent papers (Masulis et al 2011, for example) or the IRRC at http://irrcinstitute.org/contact/.