William (Bill) Chen (born 1970) is a quantitative analyst, poker player and software designer with a Ph.D. in mathematics (1999) from the University of California, Berkeley. He is currently in the Statistical arbitrage department at Susquehanna International Group.

At the 2006 World Series of Poker Chen won two events, a $3000 limit hold 'em event with a prize of $343,618, and a $2500 no limit hold 'em short-handed event with a prize of $442,511. Prior to these events Chen's previous largest tournament win was for $41,600 at a no limit hold 'em event at the Bicycle Casino's Legends of Poker in 2000.

Chen has been a longtime participant in the rec.gambling.poker newsgroup and its B.A.R.G.E offshoot. He is also a member of Team PokerStars.

With Jerrod Ankenman, Chen coauthored The Mathematics of Poker, an introduction to quantitative techniques and game theory as applied to poker.

As of 2007, his total live tournament winnings exceed $930,000.

The Chen Formula

Prior to his breakout 2006 performance, Chen authored the Chen Formula which was published in Lou Krieger's 2000 book Hold 'Em Excellence. The formula ranks starting hands by assigning them a numerical value, as follows:

1. Take the high card and score it. A=10,K=8,Q=7,J=6 and 10 to 2 = 1/2 the value of the card. (a 6 is worth 3, for example)
2. If the 2nd card pairs the first, then the value is either twice the high card point or 5, whichever is greater.
3. Round any half-points up.
4. If the cards are not paired then calculate the gap for the lower card and subtract off a gap penalty. The gap is the number of cards required to complete the sequence, for example, a 9 and 6 have a gap of 2, needing an 8 and 7 to complete the sequence:
* For a 0 gapper subtract 0.
* For a 1 gapper subtract 1.
* For a 2 gapper subtract 2.
* For a 3 gapper subtract 4.
* For a 4 gapper or more subtract 5 (includes A2,A3,A4, A5).
5. If the cards are of the same suit apply a flush bonus of +2 pts.
6. If the cards are a 0 or 1 gap and the top card is a J or lower apply a +1 straight bonus.

Then 12 - Chen Point Count in general is the Sklansky and Malmuth hand grouping. Examples:

* 8♣ 8♠: 4 pts for the first 8, double for the pair is 8 Chen points. This puts it in S&M group 4.
* 9♣ 7♣: 4.5 points for the 9, -1 for the 1 gapper, +2 for the same suit and +1 for the straight bonus. Round up to 7 Chen points which is in S&M group 5.

The following hands are the exceptions (off by 1): 55, AQs, A9, AX, 96s, 32s, 98, 97, 76.

World Series of Poker bracelets
Year Tournament Prize (US$)
2006 $2,500 Short Handed No Limit Hold'em $442,511
2006 $3,000 Limit Hold'em $343,618

Bibliography

* William Chen and Jerrod Ankenman (2006). The Mathematics of Poker. Conjelco. ISBN 1-886070-25-3.

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