The Whole-History rating system is a system designed to estimate the skill of players over time, it is loosely based on the Elo rating system.
This implementation of the Whole-History rating system contains one variable set to the following value;
The w² value is the maximum rating² per day that a fighter can change.
This rating system works by iterating over an entire set of results to work out the curve of skill level that a fighter changes over their career. Instead of working incrementally like Elo or TrueSkill, where each new result changes the involved fighter's ratings, Whole-History will update past ratings based on new information.
By working through both directions in time, it allows ratings to be adjusted retroactively based on future performances.
By retroactively adjusting ratings, a more accurate set of skill ratings can be created over the course of a career. The skill rating after the last fight being the current rating.
The Whole-History rating system does not handle draws, this implementation treats a draw as a win and a loss on the same day against the same opponent.
These ratings exclude fighters who have not fought within the last 18 months.
For more information on the Whole-History rating system, you can read Rémi Coulom's original whitepaper.
Please be aware that these ratings are calculated pound-for-pound, not per weight class. Fighters who recently switched weight class have ratings based primarily on having competed in their previous class and are not adjusted to their new class.