SafeHarborGames Rating System

Since its creation in 2008, Safe Harbor Games has become a microcosm of the online gaming community at large. It provides a community based gamming site that has attacted players from around the world and from many other gaming sites. For one group in particular, we have attracted competitive Backgammon players who not only compete in group tournaments, but also play against each other to hone their own playing skills by playing against other players who skills were equal or better than their own.

One of the first Backgammon servers to offer a way for players to rate each other was FIBS (First Internet Backgammon Server). All backgammon players on FIBS have a rating. The higher the rating, the better skilled the player is and since every player has a rating, you can easily determine whether a particular player was the one you want to play.

FIBS rating method, derived from the ELO rating system used in professional Chess, is the gold standard that many game sites, including Safe Harbor Games, has adopted for their own rating system.

Basic Principles

The FIBS rating needs five pieces of information to determine a player's rating:

  1. Current rating
    If the player has no current rating, then their rating is set to 1500.
  2. Current experience
    A new player will start out with an exerience of 0.
  3. The length of the match
    It doesn't matter how many games are played, just the total points for the entire match.
  4. The difference in ratings between the two oponents.

The ratings for most players will fall between 1000 to 2000 with the higher the rating, the better the skill, in theory.

Detailed Calculations

Our routines determine the ratings and experiences for both players when the match is over. Please note the formulas shown below are to illustrate the complexity of the calculations. The actual programmed calculation flow may be different, but the results are the same.

Required Information
  • Results - who won and lost
  • Ratings for both players.
  • Experience for both players.
  • Match Length (points) - Must be a completed match.
Assigned and calculated values.
  • n = Match Length.
  • P1 = Winner's Rating
  • P2 = Loser's Rating
  • E1 = Winner's Experience
  • E2 = Loser's Experience
  • D = Difference between the two Ratings
    abs(P1 - P2)
  • U = Probability of the underdog (lower rating) winning the match
  • F = Probability of the favorite (higher rating) winning the match
  • PE1 = Modifier based on Winner's experience
    PE1 = max(1, ((500-(E1 + n))/100))
  • PE2 = Modifier based on Loser's experience
    PE2 = max(1, ((500-(E2 + n))/100))
Calculated Results
  • Winner's change in Ratings
    + (4*PE1*sqrt((double)n)*U)
  • Loser's change in Ratings
    - (4*PE2*sqrt((double)n)*U)
  • Change in Experience
    + n
Accuracy of Ratings

There is a general belief that if you want to find a match with a player of roughly the same ability, look for someone with a similar rating, or if you want to play someone who is a better player, look for someone with a higher rating than your own. In any rated room, mouse over the player in the population list on the right side to see their rating.

This method will get you a rough idea of who to play - the greater the experience, the more accurate the ratings usually are.

Safe Harbor Games Ratings
Ratings are calculated and updated as soon as the match is complete. Unfinished rated matches are resolved by the system after 48 hours. The one difference in calculations for unfinished matches, is the loser of the match receives twice the loss of points to their ratings. This is done to encourage players to finish their matches, even if they lose the match.


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