I became curious about how rerates work after seeing an NM who reached 2200 in 2014 have his peak rating rerated down to 2199 during the migration to MUIR. This is what I got from ChatGPT:
Is this true? Let’s say player A plays in the World Open, and then plays at a small local event the week after. If player B wins against player A at the small local event, and later, it turns out that one of A’s opponents from the World Open was rerated, is there no chance that player B is rerated down a few points because player A’s rating calculations was frozen for that later event?
And considering USCF has been running rerates overnight for a few months, does that mean that if a post-event rating has stayed stable for 3 full days, that there is no chance that B loses any rating in a future rerate?
Actually, the change that caused the ratings drop on that (unnamed) NM was done two weeks prior to the move to MUIR.
During the testing of the new ratings program, we came up with several errors in the existing program, some of which dated back to its initial writing in 2004. Among the issues that were found were a faulty rounding error, issues with floors and match play limits and a one-line error in the initialization code.
Rather than have the cumulative effect of those changes be done on MUIR, we did them on the existing system, so that any changes that are seen on MUIR are directly a result of things that happened on MUIR, not the formula issues.
But this resulted in players falling below a 200 point ratings level which was also their (previous) floor. We have around 180 floor increases in the system for when we get rerates working back that far, but I don’t know how soon we’ll get there.
As to ChatGPT, you can believe what it says if you wish, I choose to think it does not understand the issues.
The two-month floating rerates that are done overnight should result in fairly stable ratings assuming no corrections are made or tardy events received and rated, but only within the context of that two-month floating window. A number of corrections have been made to events more than two months old, and we also don’t have the FIDE adjustments in the system for the last 3 months
So as the rerates work further back (they were scheduled to do one back to 1/1/2025 overnight, I haven’t checked to see how it went yet), some of those older corrections may have a ripple forward effect upon other events, but those are usually fairly small.
The reason we wait for at least one rerate of an event before awarding titles (like NM) is the ratings are usually pretty stable at that point.
Floors are a different matter, they can and do get changed during a rerate, though not very often.
The reason we put in around 180 floor increases (most of which haven’t taken effect yet because we haven’t done a rerate back that far) is that it was felt that removing a floor that has been in place for years was unreasonable.
That’s different from removing a floor that may have only been in effect for a few days or weeks, because it is unlikely a player who just earned a higher post-rating floor is likely to drop below that floor in a matter of weeks.
FWIW, we also found one OLM floor that was earned 30+ years ago but apparently not put in the system, I think we now have it in place for 2025 and beyond and eventually it will be in place going back to 2004, the current start of the rerate window.
Thank you! One final question, when you refer to the “rerate of an event”, are you referring to the daily rerates that have been carried out overnight for the past few months, or are you referring to the weekly rerates?
They’re both rerates, they just vary in the length of time they cover. The point to the overnight two-month rolling window rerate is that 99% of the events we rate are received and rated within 4 days of when they end, so this puts them in proper chronological order.
A rerate back to 1/1/2025 is supposed to run overnight tonight. Starting next week larger rerates will be run early overnight every Tuesday morning. I don’t have an ETA for when they’ll go back before 2025, though.
