Some proponents have also claimed that modern maternal mortality rates in American hospitals are often obscured by being statistically tracked under 'anesthesiology'. However, evidence suggests that if this is in fact the case, the practice is unlikely to account for more than a small fraction of maternal deaths: one study of maternal mortality records lists the "total" share of maternal mortality deaths recorded as stemming from anesthesia-related complications as just 5.2%. A study of anesthesia-related maternal mortality in the United States between 1979 and 2002 found the share of maternal mortality deaths caused by anesthesia to be just 1.6%, and that the share had dropped 59% between the time periods examined.