What is the WTN Game zONe and how does it and WTN map to NTRP?

I wasn't going to write again on this subject so soon, but the USTA sent out yet another e-mail this morning hyping WTN, so I figured no time like the present to keep the posts going.

The latest e-mail doesn't offer a lot of new information, it just reinforces that NTRP is not going away for League play as a static (for the year) rating/level is more useful for season long competition, but it does offer a downloadable PDF guide/FAQ that summarizes much of the other information out there and that I've written on before.

But on to the new content I have for today!

The USTA will soon be publishing the ITF's World Tennis Number (WTN) for players on their usta.com profile.  While the USTA is saying NTRP is staying put for USTA League, it is still interesting to look at WTN and how we might correlate it to NTRP.

NTRP is purported to offer "compatible" matches between players of the same level.  For example, two 3.5s (3.01-3.50) are considered compatible and should have a reasonably fun and perhaps competitive match with each other.

WTN has what is called the Game zONe which is the range of WTNs a player should be competitive with, in fact they state your winning percentage should be 35-65%, which would seem to be more than compatible and legitimately competitive.

So what is this Game zONe range?  Several examples appear on the WTN info pages I've seen, here is a sampling:

• WTN of 25.4 with a Game zONe of 23.6 to 27.2 (range of 3.6 from -1.8 to +1.8)
• WTN of 24.5 with a Game zONe of 22.7 to 26.8 (range of 4.1 from -1.8 to +2.3)
• WTN of 18.0 with a Game zONe of 16.1 to 19.8 (range of 3.7 from -1.9 to +1.8)

Now, perhaps none of these examples are real, and the inconsistency in the size of the range and offset  from the WTN isn't indicative of what we'll really see.  But if it is close to reality, we can perhaps figure out a mapping from NTRP to WTN and vice versa.

If the WTN "competitive" window is ~4 (+/- 2), the "compatible" window would be a bit larger, say 6 (+/- 3), and NTRP levels being on the 0.5 mean the "compatible" range for NTRP is 0.5.  Which would lead us to believe that a WTN range that is the equivalent of a NTRP level is 3.  If that is true, then there are ~13 levels (3x13 = 39) covering 40 to 1.

Note, it is possible that the Game zONe is actually somewhat variable depending on the WTN, for example, perhaps the zone gets smaller at lower WTNs, i.e. the pro level.

But another way to look at it might be that NTRP ranges from 1.5 to 7.0 and that covers 12 levels.  So if there are 12 NTRP levels and 40 rounded WTN ratings, one NTRP level should span 3.33 WTN levels which is close to the first approach above.

Taking either of these approaches as guidance, we'd have the following potential mapping of NTRP to WTN:

Hypothetical NTRP to WTN Mapping
NTRP	WTN
1.5	40-38
2.0	37-35
2.5	34-32
3.0	31-28
3.5	27-24
4.0	23-20
4.5	19-16
5.0	15-13
5.5	12-10
6.0	9-7
6.5	6-4
7.0	3-1

Note of course that NTRP isn't really used across all those levels as it isn't really calculated for players outside of the 2.5-5.5 range, so whether or not Novak would be right at 7.00 or not is unknown.  And I'm only guessing at how many slots will be reserved for beginners who don't really play competitively to actually have a rating calculated.

I've also taken the liberty of having NTRP levels from 3.0-4.5 cover 4 WTN levels each since that is where the bulk of the players are, and the fringes on the end of the NTRP scale cover 3 WTN levels each which is really just a guess on my part.  Perhaps more differentiation is needed at the pro level and those ranges are larger.

I've also done a discreet mapping from NTRP to WTN above, but the reality is that because the algorithms are different, there may be some overlap when WTNs are published.  For example there may be 3.5s that have WTNs that don't all fit nicely in the 24-27 bucket and there are some WTN 23s or 28s as well that happen to be NTRP 3.5.

So it may be that this math isn't exactly right.  But I do think it gives us a ballpark idea how things may map.  When WTNs are actually published, I will do analysis and see how things map in the real world.

The big thing players will need to get used to is that WTN is "upside down", and as you get better your rating gets lower.  I've noted this early in what I've wrote, but it probably deserves mention again.

What do you think?  If you are primarily a League player, will you follow your WTN or consider it just noise?