The International Tennis Number - What is it and how does it compare with NTRP?

Those of us that play USTA League have our ratings life centered around NTRP, the rating system used by the USTA for level based league and tournament play.  The NTRP system works well for the most part and results in competitive matches between players of similar ability.

But there are other ratings systems out there.  One from the International Tennis Federation (ITF) is the International Tennis Number (ITN).  From their Web-site:

The International Tennis Number (ITN) is a tennis rating that represents a player’s general level of play and is recognised internationally

This sounds very similar to NTRP, and from what I've read and can tell, the goals are basically the same, to have a way for players of similar ability to play more tennis and grow the game.  So what is different about the ITN?

The big thing is the scale and direction.

With NTRP, player ability increases as the rating gets larger, e.g. a 3.5 is better than a 3.0, and a 4.5 better than a 4.0, and the scale more or less goes from 2.5 to 7.0 in half point increments.

The ITN on the other hand is on a 1 to 10 scale without half point designations, but in reverse order.  A beginner is a 10, and a world class player is a 1.  Moving "up" is actually moving to a smaller numbered ITN.  This gives you 10 levels which is more or less equivalent to the 10 levels the NTRP gives you from 2.5 to 7.0.  In fact, the ITF has a conversion chart that pretty much just maps the levels one to one in opposite order.

So in the end, either system should result in a rating that lets you identify and find other players of similar ability.  But how they go about calculating the rating is entirely different.

Those that regularly read my blog know that I calculate Estimated Dynamic NTRP Ratings and do reports for players wanting to know how their rating is improving or how their results affect their rating.  I've done a little bit (an understatement) of research on how the algorithm works and have written an FAQ with a lot of good information and answers, but the short form is that the algorithm looks at the current dynamic rating of all players in the match to arrive at an expected score, and then compares this with the actual score to determine how to adjust each player's rating.  Do better than expected, your rating goes up, do worse than expected, and it goes down.  It is important to note that the score does matter, not just winning or losing as game differential is considered by the algorithm.

The ITN on the other hand documents a calculation that is more focused just on wins and losses and the level of your opponent.  For example, it calls out that a win against a same level opponent yields 1 point, a win against one level higher is 2 points, and so on.  Correspondingly, losses against at level opponents are -1, against one level down -2, etc.  Wins against lower level opponents or losses against higher level opponents are not given point values.

The ITF does not host a site or calculate a ratings for players, but outlines the above approach and recommends that ratings be updated at least yearly if not more often.  The update involves taking the player's current ITN and adjusting it up or down by the average points per match, and then rounding it.

For example, if a player played only at-level players and won 75% of their matches, they would get 0.75 points per match and regardless what level they were at, would move to the next better level.  For example purposes say a player is an ITN 7, subtracting the 0.75 would be 6.25 and rounding that would be a 6 and they would move "up" a level to their new ITN of 6.  The number of matches played and frequency of updates will obviously be a factor in how much a player can or does move.

For the most part, the two different systems track each other, but because they are calculated differently there are some deviations where players may end up with an NTRP level and ITN that are not equivalent per the conversion chart.  This doesn't mean that either one is right or wrong, they just use different criteria and so end up at a different result.  NTRP focuses on scores, ITN focuses on wins.  NTRP uses the dynamic rating of players in a match, ITN just looks at the ITN level of the players.

Where is the ITN used?  It has not really been adopted in the United States to date, but perhaps that will change.  The conversion chart linked above shows that Great Britain's system is very similar on a 1 to 10 scale but with added point levels, and from what I hear ITN is used in other European countries to some degree.

The example calculation/algorithm the ITF documents is I think intentionally simple as it was written over 10 years ago and they wanted organizations and national federations to have a low technical bar to reach to implement it.  I can think of a number of ways to improve the simple calculation and have done so as a fun comparison in the past.  If there is interest, I will perhaps publish some ratings lists using ITN or include an ITN in the reports I do.

But what do you think?  Is there a place for the ITN?  Should there be an international system rather than every country/organization having their own?  And should a rating system consider scores and actual current ratings?  Or should the focus be on wins regardless of score and just look at the level of the players?

Please leave comments here or on Facebook, or e-mail me with your thoughts.