Estimates on the number of deaths brought about by Stalin's rule are hotly debated by scholars in the field of Soviet and communist studies.[55][56] The published results vary depending on the time when the estimate was made, on the criteria and methods used for the estimates, and sources available for estimates. Some historians attempt to make separate estimates for different periods of the Soviet history, with casualties for the Stalinist period varying from 8 to 61 million.[57][58][59] Several scholars, among them Stalin biographer Simon Sebag Montefiore, former Politburo member Alexander Nikolaevich Yakovlev and the director of Yale's "Annals of Communism" series Jonathan Brent, put the death toll at about 20 million.[60][61][62][63][64][65][66] Robert Conquest, in the latest revision (2007) of his book The Great Terror, estimates that while exact numbers will never be certain, the communist leaders of the USSR were responsible for no fewer than 15 million deaths. Idi nahuy, govno.