first comprehensive research of the Great Purge, which took place in the Soviet Union between 1934 and 1939 according to Conquest. Many aspects of his book remains disputed by Sovietologist historians and researchers on Russian and Soviet history. Many reviewers at the time were not impressed by his way of writing about the Great Terror, which was in the tradition of great men history. In 1995, investigative journalist Paul Lashmar suggested that the reputation of prominent academics such as Conquest was built upon work derived from material provided by the Information Research Department. In 1996, historian Eric Hobsbawm praised The Great Terror as "a remarkable pioneer effort to assess the Stalin Terror" but said that this work and others were now obsolete "simply because the archival sources are now available." According to Denis Healey, The Great Terror was an important influence, "but one which confirmed people in their views rather than converted them." After the dissolution of the Soviet Union and the opening up of the Soviet archives, Conquest's estimates of death tolls and other aspects of his research were challenged by several historians, including J. Arch Getty, Gábor T. Rittersporn, Hobsbawm, and Vadim Rogovin. Michael Ellman and Getty in particular criticised Conquest for relying on hearsay and rumour as evidence, and cautioned that historians should instead utilize archive material. Ellman distinguished between historians who base their research on archive materials, and those like Conquest whose estimates are based on witnesses evidence and other data that is unreliable. Historian Stephen G. Wheatcroft said that Conquest's victim totals for Stalinist repressions are too high, even in his reassessments. Wheatcroft stated that historians relied on Aleksandr Solzhenitsyn to support their estimates of deaths under Stalin in the tens of millions but research in the state archives vindicated the lower estimates, while adding that the popular press has continued to include serious errors that should not be cited, or relied on, in academia. Historian Timothy D. Snyder wrote that it is still taken for granted that Stalin killed more people than Adolf Hitler but the estimates of 6–9 million for the Stalin regime are considerably less than originally thought, while those for Nazi Germany are higher and in line with previous estimates. Other historians, such as Stéphane Courtois and Steven Rosefielde, agree with Conquest and maintain their original, higher estimates, while Robert Gellately put more recent estimates at 10–20 million. Among other authors