The problem is what do you consider "killed by Stalin." This is the major problem with death toll questions. Do you consider a famine caused by bad agricultural policies as "killing"? Does the person have to be specifically killed by direct order to be considered?

That is the problem with the estimations on death toll. This is not helped by the fact that major publications prior to the fall of the USSR was overly estimated and the actual KGB records point to something far less. The conservative estimates for the Great Purge, which was direct killing of political enemies, is around 200,000. Although Robert Conquest estimated it at an incredible 10 million. Also people who tend to care about death tolls like adding in the holodomor to inflate the numbers, whereas I would tend to say indirect killing by bad social policies does not really equal to the same type of killing such as the holocaust.

In a previous post by mine and this is what I had to say about estimations on Stalin's death toll.

Therefore he is the poster boy for the massive 20-30 million death toll that is often tossed out whenever someone mentions Hitler's death toll. The truth is a tad more murky, than Conquest or the preachers of the Stalin is worst than Hitler choir. Timothy Snyder, author of the book Bloodlands estimates that the total is actually around 6 million. That is including the deaths related to the Famine of 1932. If you look directly at those killed deliberately/with purpose, it would be around 3.5 million (estimated). The reason I would split the two numbers is because of the belief that outright killing someone with purpose is different than starvation based on policy decisions. However, even ignoring that distinction the numbers are only 1/4 of Robert Conquest's original claim, and a 1/3 of the "revised" claim. Yet the numbers now being discussed by recent historians all tend to hover around the lower estimates, however the popular misconception still is relying on a historian that figures have been debunked.