Rummel was the author of twenty-four scholarly books, and published his major results in "Understanding Conflict and War" (1975–81). He spent the next fifteen years refining the underlying theory and testing it empirically on new data, against the empirical results of others, and on case studies. He summed up his research in "Power Kills" (1997). Other works include "Lethal Politics: Soviet Genocides and Mass Murders 1917–1987" (1990), "China's Bloody Century: Genocide and Mass Murder Since 1900" (1991), "Democide: Nazi Genocide and Mass Murder" (1992), "Death by Government" (1994) and "Statistics of Democide" (1997). Extracts, figures, and tables from the books, including his sources and details regarding the calculations, are available online on his website. Rummel also authored "Applied Factor Analysis" (1970) and "Understanding Correlation" (1976).