Summary for the WN8 Rating System for World of Tanks


2019/07/04: My (i.e. Taugrim’s) comments are in italics throughout this post.

I’m posting a copy of the “WN8 Summary” page that used to exist on http://wiki.wnefficiency.net/. It looks like that domain is no longer around. I take no credit for WN8 nor for the content below.

What is WN8? It’s the last version of the community-derived rating system for World of Tanks (WoT). WN stands for “Weighted / Normalized”.

Intro

WN8 is the latest iteration of the WN8* (WNx) project lead by Praetor77.

WN8 seeks to measure the observable contribution to matches, across an account, and hopefully infers some information about the latent variable “skill”. WN8 should not be considered the end-all-be-all of skill evaluation. It is intended to be looked at next to win-rate, battle count, average tier, and will never replace the inspection of the Service Record or platooning with someone or watching their replays. This is because WN8 cannot capture things like timing, target priority, teamwork or decision making abilities.

For a full explanation of WN8 go here.

Main differences with WN7

2019/07/04: The comparison to WN7 is dated at this point given that WN8 was introduced back in 2013. Feel free to skip this section.

  • WN8 has much more weight on damage than on kills, which was reversed in WN7. What allowed us to put more weight on damage was that WN8 uses per-tank normalization instead of the average tier-based normalization WN7 used.
  • Per-tank normalization in WN8 now allows a fair comparison of players playing only highly effective tanks for their tier (think Wft100, Foch155, Hellcat, T49, T18, T29, the old Su-26, etc.) versus players who have played many lines, with many tanks.
  • Due to per-tank normalization, light tanks and SPGs are now more fairly compared to other tank types in WN8 (they received lower WN7 than other tank types). Despite not being able to use spotting damage, WN8 expects less damage of light tanks, while WN7 expected the same as other tanks of the same tier.
  • No tier-based penalty is introduced. Low tier tanks are measured fairly against high tiers, whereas in WN7, you could raise your score artificially by playing a mix of low and high tiers, and were penalized if you only played low tiers. However, you are expected to do VERY well in low tiers to gain WN8 points as opposed to playing high tiers.
  • Scale has changed. See below.

Interval/Ratio scale explanation

WN8 uses a different scale from WN7. WN7 values ranged from 400-2800, and we turned this scale into a ratio scale, which brings about numerous advantages. Debatably the most important one after improved accuracy in measurement is that we can now say that a 2400 WN8 player on average contributes twice as much for his team to win than a 1200 WN8 player. This was not true for any rating before WN8.

2019/07/04: The important advantage noted above is key IMO – ratings that reflect relative contribution to winning are helpful for the sake of comparing how much players tend to contribute to winning.

Per-tank stats explanation

Briefly, what we have done is used vBAddict database (more than 1 million tanks played by about 20000 players) to calculate balanced and comparable “expected” values for each tank. This table is available here: http://www.wnefficiency.net/wnexpected/

2019/07/04: The XVM Mod community took over the daily calculation of “expected” values for each tank, starting back on 2017/10/08. You can find the current values and links to the previous daily values here: WN8 Expected Values

The number of games you have played on each tank allows us to estimate what your “expected” total stats should be for your entire account. Then your actual total stats are compared to the expected stats ( rSTATS), which are then normalized and adjusted to a baseline (rSTATSc), and these numbers are then input into the formula shown below. rSTATSc are capped to prevent, for example, farming spots on tanks with low expected value of spots, like arty.

Brief explanation of the formula and how it was devised (Eureqa)

Using a subset of the noobmeter.com database (115k players), we used their stats as input to a program called Eureqa which uses genetic algorithms to find the best “formula” to explain winrate using the rest of the stats. So, Eureqa assigns weights to each stat according to how important it is in determining wins. The final formula is:

WN8 = 980*rDAMAGEc + 210*rDAMAGEc*rFRAGc + 155*rFRAGc*rSPOTc + 75*rDEFc*rFRAGc + 145*MIN(1.8,rWINc)

2019/07/04: Some key notes about the formula:

  1. The formula includes damage, frags (kills), spots, defense points, and win rate. These stats are available at the per-tank level in the WoT API and in particular the first four correlate with winning, based the massive data regression that was performed by the WN team
  2. WN8 is calculated at the tank level, and WN8 is calculated at the account level (as an aggregate of your performance in all the tanks you’ve played)
  3. Cap points were not found to be statistically correlated with winning
  4. People unfamiliar with the formula often accuse Unicums of being “redline snipers”. However, the WN8 authors noted the following:

    So, rSPOT*rFRAG appear to measure something important for winning. These interactions seem to be properly measuring players that can do multiple things and adapt to what needs to be done to win as opposed to players who play absolutely safe, and simply deal out damage (rDMGc only).

    Per player analysis indicated (and Eureqa agrees apparently) that rFRAGc *rSPOTc can tell you a lot about how much a player actually manages to win. The authors believe it has to do with aggresiveness and willingness to create opportunities for the team. If you are solidly getting high rSPOTSc values, you are putting yourself in more risky positions on the map, and if you are doing so while maintaining high avg frags, damage, defense and wins, IMHO you are a better player than if you manage the same damage and frags sitting in the back and shooting targets your teammates light up. The most often repeated advice in this game is “get your gun in the game and stay alive to keep it there”, and rSTATc values appear to support that advice.

  5. People often ask why assisted damage is not included in WN8, and one reason is that it is not available at the per-tank level in the WoT API (Application Programming Interface). Check the section on Random Battles for player vehicle data. Obviously you can see the assisted damage for each tank in-game, but if it’s not in the API, 3rd party web sites and mods have no ability to access that stat

2019/07/04: For most players, the summary provided above is sufficient for framing what WN8 is. Of course, there is a lot more depth in terms of how the WNx project derived WN8. You can find much more detail about WN8 with the following links to the WoT Wiki and Wayback Machine:

At some point I may post the FAQs on my blog so that content is not lost. From what I can tell, Google doesn’t index content on the Wayback Machine so discoverability of the FAQs is an issue.

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Posted in World of Tanks

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