Note: Issues and Countermeasures Arising from the Correspondence Between Ratings and Shogi Ranks

[Honey-Mint]

This was a very good update!

What particularly stands out this time are:
・Unification of ratings
・Introduction of ranks
These two points.

These are very interesting, and I expect Lishogi to move in a positive direction.

Now, many shogi sites have faced problems with these systems and implemented countermeasures.
I'll summarize what I know about these issues and conclude with a few personal suggestions.

(1) Issues and Current State Arising from Rating Unification

With the exception of 81Dojo and Shogi Club 24, platforms like Shogi Wars and Shogi Quest maintain separate rankings based on time control rules.
This stems from differences in gameplay mechanics; unifying these could risk obscuring players' strengths and weaknesses.

An article has pointed out that Shogi Club 24 faced this very problem.
https://shogi.zukeran.org/2016/05/27/shogiclub24-rating/
According to this article, separate groups emerged for the 15-minute time control and the rapid play group. This led to divergence due to separate inflation and deflation in their respective rating systems.

Perhaps in response to this, 81Dojo addresses it by applying a coefficient to rating fluctuations based on time control.
(For example, x1.11 for 10 min / 30 sec Byoyomi, x0.85 for 30 sec Byoyomi)

(2) Problems Arising from Linking Ranks and Ratings and the Current Situation

It is well known that linking ranks to ratings causes rank deflation.
Reference: https://hidetchi81.blog.jp/archives/12993833.html
For example, when a 1-dan player defeats a 3-dan player, we want to promote only the 1-dan player to 2-dan, recognizing their improvement. However, under the rating system, both players move closer to 2-dan.
This is because ranks in shogi are often perceived as indicators that are difficult to be down.

Deflation countermeasures on major sites are as follows:

• 81Dojo
  https://81dojo.com/documents/Rating_System
  For matches with large rating differences, the system adjusts so that when the lower-rated player wins, the rating change is larger, and when the higher-rated player loses, the rating change is smaller.
  Furthermore, when a rank change is imminent, the system pauses the player's progress with an “upgrade-deciding match” or “downgrade-deciding match.”

• Shogi Wars
  https://shogiwars.heroz.jp/qa?locale=ja&category=faq&num=10
  This system uses both a rank achievement rate and an internal rating, which are linked.
  Even if your internal rating keeps dropping and your achievement rate reaches 0%, your rank won't decrease unless you lose 500 games.

(3) Suggestion

Based on the above, I suggest implementing the following specifications:

• Prevent rank from decreasing for 100 matches after a rank increase. Rating decreases.
• Introduce coefficients similar to those used in 81Dojo, aligned with previous metrics like Classic and Rapid.

Naturally, there are likely various approaches.
If implementing such specifications, be sure to include them in the FAQ.