According to Klas-Göran Karlsson, discussion of the number of victims of Communist regimes has been "extremely extensive and ideologically biased." Any attempt to estimate a total number of killings under Communist regimes depends greatly on definitions, ranging from a low of 10–20 millions to as high as 110 millions. The criticism of some of the estimates, especially those of Rummel and "The Black Book of Communism" which made use of Rummel's estimates and analysis, are mostly focused on three aspects, namely that the estimates were based on sparse and incomplete data when significant errors are inevitable; that the figures were skewed to higher possible values; and that those dying at war and victims of civil wars, Holodomor and other famines under Communist governments should not be counted. According to Anton Weiss-Wendt, any attempts to develop a universally-accepted terminology describing mass killings of non-combatants was a complete failure.