He estimates that because of these reasons in 350 AD there were 33.9 million Christians or 56.5% of estimated population of 60 million.
This is a mere mathematical extrapolation by sociologist Rodney Stark. For what it's worth, even using Stark's estimate, he shows the Christian population at 10.5% in AD 300, immediately before the reign of Constantine, and at 56.5% in AD 350, which is 13 years after the death of Constantine. So even if we assume these numbers are close to correct (and they seem to be a stretch based on what actual classical historians have posited), they still show Christianity to be a significant minority (less than 20%) at the time Constantine saw the cross in the sky in AD 312.
Here's what Cambridge History of Christianity has to say:
“The figures proposed by Hopkins, MacMullen and
Stark are optimistic, but do not support a radical reinterpretation. Recent epigraphic discoveries have, if anything, suggested a more gradual winding down of the pagan cults than Geffcken supposed, and even continuity at some shrines until the end of the fourth century. The empty temples and dead gods are now seen more as a symptom of economic readjustment in the later third century caused by barbarian pressure on the frontiers, militarization of the civil service and an increased demand for revenues, particularly under the tetrarchy. This was the political background to the Christians’ rise to
between 5 and 10 per cent of the empire’s population c. 300."
~
Trombley, The Geographical Spread of Christianity, in Cambridge History of Christianity, Volume 1: Origins to Constantine.
Sir, the point was that there were a lot of Christians and Constantine could have stuck his political finger into the wind and saw which way it was blowing.
Personally, I think it was much higher because of the reactions of different provinces. All of them saw that the number of Christians in their regions was high and sought to either get rid of them or befriend them. But nobody ignored them.
And all I said was that there were studies done. You might disagree with them, but studies were one and I showed one of them.