Many of Facebook's most popular games are reporting drastically reduced audience numbers ever since the social network introduced new changes to its counting methodology, which were implemented three weeks ago in an attempt to more accurately reflect the usage of applications.

Zynga's CityVille, for example, may still be the most popular game on the site, but it's no longer the most popular application -- that honor belongs to Mensing's user profile customization app Static HTML: iframe Tabs, which boasts 61.9 million monthly active users.

The Sim City-esque game currently has 52.7 million monthly players, a significant drop from the 76.1 million that was reported just a month ago under Facebook's old counting formula -- and nearly half of the title's record high of 100+ million monthly users in January of this year.

At #2 is The Sims Social by Electronic Arts and Playfish, which has 36.5 million players now, compared to 66.2 million four weeks ago. Zynga's recently launched Adventure World has also taken a big hit, slipping from #3, when it had 37.6 million users, to now #7 with only 11.4 million.

Zynga titles still dominate the social network, though taking seven of the top ten spots on the App Leaderboard for games: virtual card game Texas HoldEm Poker rises from #5 to #3, despite going from 31.6 million monthly players in early October to a slightly smaller 30.3 million.

FarmVille kept it's #4 spot with 29.1 million users (down from 35.1 million), followed by Empires & Allies with 19.6 million (down from 26.8 million), Mafia Wars 2 with 15.2 million (launched in mid-October), the aforementioned Adventure World, and Words With Friends with 11.2 million (down from 12.5 million).

And at #9 and #10 with equal numbers, there's Disney and Playdom's Gardens of Time with 10.5 million players (down from 14.4 million), and Wooga's Diamond Dash (down from 12.4 million). You can see the full list of the top 20 Facebook games along with exact monthly active user counts.

All charts and data are courtesy of Facebook application metrics and trends site AppData.