It's not explicitly clear where the figure comes from but SuperData's MMO earnings data is compiled from "the monthly spending of 36.9 million digital gamers, worldwide, collected from developers, publisher and payment service providers". Presumably the ESO figure comes from the same place.
Game-publisher Bethesda hasn't released sales or subscription data for The Elder Scrolls Online, and as its parent company ZeniMax Media is privately held, doesn't really have to.
Only the PC version of The Elder Scrolls Online has been released so far, with PS4 and Xbox One versions to follow... at some point. The console games were delayed by six months back in May, which puts them roughly in November's ballpark. Will ongoing improvements to the PC game impact that? We haven't heard anything for a while.
The SuperData report also highlighted Star Wars: The Old Republic, which is making quite a lot of money don't you know - $165m in 2013, apparently.
The leader of subscription-based MMOs - those with a subscription as well as micro-transactions and all that stuff - is, by a country mile, World of Warcraft, dominating 36 per cent of the market and earning more than $1bn in 2013.
Lineage - to put that into perspective - is second with $253m earned in 2013.