James Liebman, a professor of law at Columbia Law School, stated in 1996 that his study found that when habeas corpus petitions in death penalty cases were traced from conviction to completion of the case that there was "a 40 percent success rate in all capital cases from 1978 to 1995." Similarly, a study by Ronald Tabak in a law review article puts the success rate in habeas corpus cases involving death row inmates even higher, finding that between "1976 and 1991, approximately 47 percent of the habeas petitions filed by death row inmates were granted." The different numbers are largely definitional, rather than substantive. Freedam's statistics looks at the percentage of all death penalty cases reversed, while the others look only at cases not reversed prior to habeas corpus review.
Try to answer this question if possible (otherwise reply "unanswerable"): According to Liebman, about what percentage of death penalty habeas corpus petitions were successful between 1988 and 1999?
unanswerable