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Informal but detailed explanation of Larsen-Silliman rating system **Long**
Posted By: Barry Silliman In Response To: Questionniare (Leonardo Jerkovic)
Date: Saturday, 20 February 2016, at 4:19 p.m.
Here is an informal, yet detailed, explanation of the Larsen-Silliman ratings system. Questions or comments are welcome.
It is not actually based on USBGF Master points, but it uses a formula similar to how USBGF Master points are allocated. (More on that below).
We are only rating ABT events, and at the ABT events, only the three divisions where ABT points are awarded. For example, most ABT events include an OPEN level (highest strength), ADVANCED level, and NOVICE level.
We award the same number of points per event that the ABT awards, only we distribute them differently. ABT points are only given to players who cash, which are usually from 1/5 to 1/8 or fewer of the entrants. We use a formula that can award points to up to, but not exceeding, half of the entrants.
For traditional bracketed events, we will slot those who cashed the same way that the ABT does for points- that is, the winner is 1st place, the runner-up and the consolation bracket winner are tied for second, the main bracket semifinalists, the consolation bracket runner-up, and the last chance bracket winner are tied for the next slot (assuming all these positions "cash"), etc. Then we go to the last chance bracket and for those who didn't cash, we slot the players further down the list.
For illustration, suppose 7 players cashed- the Main bracket winner, runner-up, and 2 semi-finalists, and the Consolation bracket winner and runner-up, and the Last Chance bracket winner. We would then slot the last chance runner-up in the #8 slot, The two last chance semi-finalists in the #9-#10 slots, the four last chance quarter-finalists in the #11-#14 slots, the eight players who lost in the Last Chance round of 16 the #15-#22 slots, etc. If in any round causes the number of slots to exceed half of the entrants, we stop and we don't give points for that round. For example, in the preceding example, if there were 44 entrants, the #15-#22 slots would get points but if there were 43 or fewer entrants, they do not get points. For Swiss-style tournaments we group the players by won-loss record and similarly apportion the points so that up to but not exceeding half the players receive points.
Where the similarity to USBGF points come in is that we use a similar formula. First place is awarded a value of 1, 2nd place a value of .7, 3rd place a value of 1/2, 4th place a value of 1/3, 5th place a value of 1/4, etc. That is, For n>2, the value is 1/(n-1). These values are summed up for the n players who cash, and each player receives their value divided by the sum, multiplied by the number of players. Then, similar to how ABT points are awarded, those in ADVANCED receive half of that amount, and those in NOVICE receive a quarter of that amount.
So we award the same number of points as the ABT does- 1 point per player at the OPEN level, half a point per player at the ADVANCED level, and a quarter of a point at the NOVICE level.
To derive the final rankings, we do some further adjustments- we only rank the last five years, but more recent years are weighted higher- both 'events' played and 'points' are multiplied by the square root of 5 for the most recent twelve months, by the square root of 4 for 12-24 months ago, the square root of 3 for 24-36 months ago, the square root of 2 for 36-48 months ago, and the square root of 1 (I forget at the moment the exact value of that) for 48-60 months ago. We call these values after these alterations "weighted events" and "weighted points". By rating more recent events more, we hope to encourage attendance.
We then provide one final adjustment to the values- if a player hasn't played in many events, their rating (which is simply weighted points divided by weighted events) could be reduced further. We added this to also hopefully encourage attendance.
Additionally, for those events that allow re-buys, players who do a re-buy are charged some fraction of an 'event' for each re-buy. We use 0.7 for most re-buys, e.g. in this case if a player re-buys one time they will be assigned 1.7 events for that event instead of 1.
The reason we only weigh the ABT events and not side events like Jackpots is because we hope that going forward more ABT directors will use this system for eligibility criteria for the lower divisions, e.g. to force a player who is doing quite well to move up from ADVANCED to OPEN, so we do not want the ratings to be influenced by side events that often have players from a mixed pool of OPEN/ADVANCED/NOVICE players.
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