Before there were such things as CHONE, Pecota, and Bill James' annual projection for players, there was a charming little thing called Similarity Scores, also created by Bill James. If you look at baseball-reference.com, you will find a description of the formula used for similarity scores and a credit to James' book The Politics of Glory; however, I first read about them in The Bill James Baseball Abstract 1986, in which he introduced the concept, having worked on it over the past year. This was also the book that introduced me to the term sabermetrics, among other things.
I stumbled across The Bill James Baseball Abstract 1986 while looking in a book store for a book that contained all the major league statistics for the 1985 season (no baseball-reference.com in those days), which I needed to prepare for a Strat-O-Matic baseball draft. (I went with a HR friendly ballpark and loaded up on power, defense be damned, and drafted Pedro Guerrero #1 at 3B/1B.) The book was an eye-opener in many ways and made me aware that there were a lot of ways to look at baseball and baseball statistics than just the traditional versions. I wonder if I would have even gravitated toward the baseball blogs that I enjoy so much today had I never crossed paths with James' Abstract. By the way, in the Dodgers chapter, James defends Lasorda's decision to pitch to Jack Clark.
If you didn't read the formula in the link, the brief version is that 1000 is a perfect match between two players. Points are then deducted from there based on differences in position, a bunch of counting statistics (e.g., hits) and a few ratios (e.g., batting average, ERA). Obviously, the higher the number, the better the match.
At baseball-reference.com, they calcluate the similarity scores on each player's page, giving the top-10 career similarities, plus the top-10 at each age of the player's career, near the bottom of the page. For example, if you scroll toward the bottom of ex-Dodger Shawn Green's player page, you'll find that his number one match in career similarity score is ex-Dodger Reggie Smith at 945. This is what similarity scores (using this formula) seem to work best for, evaluating player production over an entire career, which is good for things like Hall of Fame arguments. You'll also see that at age 29, after his last great season (2002), the 29-year old he was most similar to was Dale Murphy with a similarity score of 942.
Similarity scores don't make for a particularly great projection system, because, among other things, the stats used aren't the best for that purpose and the similarities don't account for trends (i.e., improving or not), but I'd bet that Bill James used similarity studies with different stats in play to fine tune his projection system. However, that doesn't stop the age-based similarity score summaries at baseball-reference.com from being a lot of fun to peruse and to compare current players to players throughout baseball history and see how that current player might turn out. This turns out to be a fine time to do such a thing because a) the season is over and the hot stove is still thawing out, and b) baseball-reference.com just updated them all to include the 2009 season data.
After the jump are similarity score summaries for the selected returning Dodger players at their 2009-season age. These show the top ten similar players at the same age - some of the names may surprise you:
UPDATE - corrected lists for Russell Martin, Rafael Furcal, and Casey Blake. The previous lists were incorrect due to a bug regarding position adjustments in the baseball-reference.com software that was present at the time this article was originally written. I left the incorrect tables below as well, just for the curiosity of seeing things like Bobby Grich in Russell Martin's list.
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Similar Player | Similarity Score | Similar Player | Similarity Score | Similar Player | Similarity Score | ||
Thurman Munson | 966 | Aaron Boone | 938 | Craig Biggio | 934 | ||
Sammy White | 956 | Melvin Mora | 930 | Jay Bell | 921 | ||
Ray Fosse | 942 | Jim Hickman | 911 | Tony Fernandez | 910 | ||
Ed McFarland | 941 | Dave Hollins | 910 | Ray Durham | 900 | ||
Rich Gedman | 933 | Charlie Maxwell | 909 | Barry Larkin | 895 | ||
Yadier Molina | 932 | Jim Lemon | 908 | Cristian Guzman | 893 | ||
Benito Santiago | 932 | Mel Hall | 907 | Herman Long | 887 | ||
Jack Clements | 930 | Hoot Evers | 905 | Orlando Cabrera | 885 | ||
Tim McCarver | 926 | Jay Payton | 903 | Lou Whitaker | 885 | ||
Bob O'Farrell | 926 | Kevin Millar | 902 | Frankie Crosetti | 885 |
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Similar Player | Similarity Score | Similar Player | Similarity Score | Similar Player | Similarity Score | ||
Thurman Munson | 971 | Jeff Bagwell | 975 | Craig Biggio | 944 | ||
Felipe Lopez | 966 | Ted Kluszewski | 974 | Ray Durham | 940 | ||
Mike Andrews | 963 | Alvin Davis | 960 | Jay Bell | 921 | ||
Sammy White | 962 | Joe Hauser | 948 | Lou Whitaker | 920 | ||
Ray Durham | 960 | Babe Young | 943 | Jason Kendall | 920 | ||
Lonny Frey | 960 | Rafael Palmeiro | 939 | Delino DeShields | 916 | ||
Gil McDougald | 960 | George Kelly | 939 | Chuck Knoblauch | 915 | ||
Aaron Ward | 954 | Steve Garvey | 939 | Brian Roberts | 914 | ||
Bobby Grich | 953 | Joe Adcock | 936 | Tony Fernandez | 910 | ||
Barry Larkin | 951 | Adrian Gonzalez | 935 | Paul Molitor | 909 |
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Similar Player | Similarity Score | Similar Player | Similarity Score | Similar Player | Similarity Score | ||
Aaron Boone | 938 | Ken Griffey, Jr. | 857 | Willie Wilson | 943 | ||
Melvin Mora | 930 | Jimmie Foxx | 849 | Clyde Milan | 916 | ||
Jim Hickman | 911 | Frank Robinson | 840 | Max Carey | 910 | ||
Dave Hollins | 910 | Rafael Palmeiro | 813 | Duff Cooley | 908 | ||
Charlie Maxwell | 909 | Barry Bonds | 812 | George Case | 904 | ||
Jason Varitek | 909 | Gary Sheffield | 811 | George Burns | 903 | ||
Jim Lemon | 908 | Jim Thome | 811 | Steve Brodie | 896 | ||
Mel Hall | 907 | Jeff Bagwell | 810 | Ginger Beaumont | 892 | ||
Hoot Evers | 905 | Chipper Jones | 803 | Harry Hooper | 884 | ||
Jay Payton | 903 | Willie Mays | 800 | Mickey Rivers | 873 |
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Similar Player | Similarity Score | Similar Player | Similarity Score | Similar Player | Similarity Score | ||
Nick Markakis | 971 | Richie Zisk | 971 | Britt Burns | 972 | ||
Carlos Beltran | 961 | Bobby Higginson | 970 | Moe Drabowsky | 971 | ||
Vernon Wells | 960 | Sam Chapman | 966 | John Henry Johnson | 971 | ||
Enos Slaughter | 955 | Aubrey Huff | 962 | Jack Fisher | 970 | ||
Ellis Burks | 954 | Jacque Jones | 961 | Carl Cashion | 970 | ||
Bobby Bonds | 945 | Bill Nicholson | 959 | Ken Holtzman | 969 | ||
Ellis Valentine | 944 | Jim Edmonds | 957 | Norm Baker | 968 | ||
Rocco Baldelli | 944 | Jason Giambi | 957 | Jerry Walker | 966 | ||
Bug Holliday | 941 | Larry Doby | 953 | Dontrelle Willis | 966 | ||
Andre Dawson | 938 | Reggie Sanders | 951 | Mike Witt | 965 |
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Similar Player | Similarity Score | Similar Player | Similarity Score | Similar Player | Similarity Score | ||
Ray Culp | 977 | Masato Yoshii | 966 | Doug Bird | 961 | ||
Pedro Martinez | 975 | Sig Jakucki | 959 | Chad Cordero | 958 | ||
Jake Peavy | 973 | Walt Dickson | 957 | Roger McDowell | 958 | ||
Stan Williams | 970 | Kenshin Kawakami | 950 | Huston Street | 956 | ||
Sid Fernandez | 966 | Frank Oberlin | 949 | Victor Cruz | 956 | ||
Carlos Zambrano | 965 | Jimmy Zinn | 948 | Steve Bedrosian | 953 | ||
Dennis Martinez | 965 | Lou Tost | 946 | Antonio Osuna | 953 | ||
Scott Kazmir | 963 | Art Delaney | 946 | Luis DeLeon | 953 | ||
Dave McNally | 961 | Bob Keegan | 945 | Scott Williamson | 951 | ||
Ramon Martinez | 959 | Tom Filer | 944 | Tom Niedenfuer | 950 |
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Similar Player | Similarity Score | Similar Player | Similarity Score | Similar Player | Similarity Score | ||
Hank Aguirre | 982 | Ricardo Rincon | 967 | Scott Sullivan | 988 | ||
Rich Folkers | 981 | Pedro Feliciano | 962 | Jack Wisner | 985 | ||
Gene Walter | 978 | Rich Rodriguez | 960 | Gary Wagner | 984 | ||
Juan Agosto | 977 | Tony Castillo | 956 | Roy Thomas | 984 | ||
Dick Kelley | 976 | Steve Frey | 950 | Jack Billingham | 984 | ||
Greg Cadaret | 975 | Kerry Ligtenberg | 949 | Brandon Medders | 982 | ||
Rafael Perez | 975 | Graeme Lloyd | 949 | Bobby Locke | 982 | ||
Ken Frailing | 975 | Tom Hilgendorf | 946 | Hersh Freeman | 981 | ||
Pedro Martinez | 975 | Mike James | 943 | George Frazier | 981 | ||
Dave Leiper | 974 | Jim Hughes | 942 | Toby Borland | 981 |
Did I acknowledge baseball-reference.com enough?