Ranking systems
There have been three ranking systems used in Allegiance. The most recent, AllegSkill, is being used on the live servers.
ELO
This was the first statistical rating system that was tried in Allegiance. The basic ELO rating system is well described on Wikipedia. However, ELO was developed for games of 1 vs 1, like chess. To use it for Allegiance, a team's ELO points was simply the sum of all the players' ELO points on that team. Then post-game adjustments were calculated using the ELO equation and applied to all players.
One major downside of ELO is that it's a zero-sum game. What one player gains, another player loses. Since we have a constant influx of newbies who might lose a few games and then leave forever, this meant that ranks would gradually drift over time. Also, Alleg's ELO system became more and more complex when dissatisfied players tried to "fix" it. Newbies actually started with rank 15 (1500 ELO points), but the displayed rank in-game was reduced by a number based on how long they played. Players ranked as expert and above had penalties that kept their ranks artificially low.
HELO
In a bold move to simplify the rating system issue, Pook implemented a new version, based on the ranking system of HALO 2. It's detailed in one of his blog posts and the source code can be found in this forum post. You can read more about the HALO EXP ranking system here and here.
This is not a zero-sum system, which means that ranks are more stable over time. However, it has other flaws. When calculating the adjustment of Bob the pilot's rank after a game, it only looks at the players on the opposing teams. It doesn't take into account what other pilots were on Bob's team. This makes the HELO ranks less accurate.
In addition, HELO ranks are not guaranteed to be mathematically sound. How can we know that one inter. 6 is worth twice as much as a novice 7 when autobalancing? This issue could be mitigated by studying the outcomes of autobalanced games and carefully adjusting the rank thresholds (the right-most conversion table on the leaderboard.
Criticism
Both ELO and HELO have been criticized because players can inflate their rank by stacking (ie. consistently joining the team that is most likely to win), and that this makes the ranks meaningless. Other players argue that this could be mitigated by using auto-balance more often.
AllegSkill
This is a replacement for HELO that was developed by Sgt_Baker et al.. It is based on Trueskill, which was developed by Microsoft Research to address some flaws in the HALO 2 ranking system.[1]
Trueskill is used for all online matchmaking on XBox 360.
AllegSkill is now live and supplies the ranks seen in the game.
