Hanke employs a unique methodology, based on the principle of purchasing power parity, which allows him to accurately estimate inflation in countries with very high inflation rates. Using this methodology, Hanke and his collaborators discovered several cases of hyperinflation that had previously gone unreported in the academic literature and popular press. These include the 1923 hyperinflation episode in the Free City of Danzig, and more recently, suspected cases in North Korea (2011), and Iran (2012). In 2012, Hanke and Nicholas Krus documented all 56 cases of hyperinflation that have occurred in history, in "World Hyperinflations," a chapter in the Routledge Handbook of Major Events in Economic History." Since then, Hanke has documented two additional cases of hyperinflation: One occurred in Venezuela in 2016, and the other occurred in Zimbabwe in 2017.