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The database has been updated with 2011 offensive stats. Congratulations to Jose Reyes, Shane Victorino, and Dexter Fowler who were among the most dominant triples-hitters last year, and to Miguel Cabrera and Jose Bautista whose on-base percentages were among the most dominant of all time.


The goal here is not to duplicate excellent resources like Total Baseball or The Baseball Encyclopedia, but to take the same data and present it in a way that shows different relationships, yields new insights, and raises new questions. The focus is on putting single season stats in a historical context and identifying the truly outstanding player seasons, not just those with big raw numbers. My method is primarily the z-score (see below for a simple explanation) and a few kinds of charts, all hyperlinked for easy cross-referencing.

Game of Chance is a 10-minute baseball podcast. Every week I talk about current events and my thoughts about baseball in general, with a focus on statistics and historical context.

Historical Graphs

Historical Graphs

Show trends of statistics through the years.

Home Runs 1905-1970
Stolen Bases 1872-1950
Batting Average 1907-1955

Player Pages

Player Pages

Single season z-stats for every player.

Ty Cobb 1915
Tony Gwynn 1995
Todd Helton 2000

Season Stat Charts

Season Stat Charts

Statistical analysis of totals for every season.

2004 National League
1961 American League
1927 American League



All-time best single season z-scores.

Runs Created
Home Runs
At-Bats per Strikeout

Stats Glossary

There are a few statistics in use on this site that may not be familiar to you. Here are explanations of the least common ones.

AB/K - At-Bats per Strikeout
Number of at-bats it takes for player to strike out (AB / SO).
ISO - Isolated Power
A measure of ability to get extra base hits (SLG - AVG).
RC - Runs Created
An excellent measure originally devised by Bill James to estimate the number of runs a player has contributed to his team through his offensive performance. I use the 2002 version of the formula without situational hitting data.
SBR - Stolen Base Runs
A very approximate measure of how many runs a player's basestealing adventures have earned his team (.3*SB - .6*CS).

If there are any other stats you'd like to see on this site please let me know.

What's a Z-Score?

The z-score is a statistical measure of how a particular number compares to the average. Technically it is the number of standard deviations from the mean, but one need not have a complete mathematical understanding of the z-score to appreciate that it shows how a given player performs compared to the competition.

For example, if the league average for home runs is 9 and a player hits exactly 9 home runs, his z-score is zero. If he hits more than 9 HRs his z-score will be positive and if he hits fewer than 9 it will be negative. Precisely how positive and how negative will depend on how other players in the league fared. For example:

  • In the National League in 2001 the league average for home runs was about 12. The leaders:
    1. Barry Bonds 73
    2. Sammy Sosa 64
    3. Luis Gonzalez 57
    Several others also exceeded 40. Bonds' HR z-score was +5.20.
  • In the American League in 1920 the league average for home runs was about 4. The leaders:
    1. Babe Ruth 54
    2. George Sisler 19
    3. Tilly Walker 19
    4. Happy Felsch 17
    Nobody else exceeded 12. Ruth hit nearly three times as many HRs as anyone else (in fact, he alone hit more than any team beside the Yankees), so his HR z-score was +8.45 which shows mathematically what we see intuitively: that his performance was more dominant than that of Bonds in 2001.

These two examples deal with some of the most extraordinary numbers of all time, but usually league leaders need not have such high z-scores. Also, certain statistics (like HRs and IBBs) are prone to higher z-scores than others. For example, the z-scores of recent American League OB% leaders:

Year Player OBP Z
2001 Giambi .477 +3.50 (6th all-time)
2002 Ramirez .450 +3.11 (25th all-time)
2003 Ramirez .427 +2.35
2004 Mora .419 +2.14

In short, z-score is a measure of a player's dominance in a given league and season. It allows us to compare players in different eras by quantifying how good they were compared to their competition. It it a useful measure but a relative one, and does not allow us to draw any absolute conclusions like "Babe Ruth was a better home run hitter than Barry Bonds." All we can say is that Ruth was more dominant in his time.

About the Computations

To compute the league stats (mean, maximum, standard deviation, skewness, etc) I have used data from all players with at least 0.5 plate appearances per team game. For appearing on a z-leaderboard or having a season page the minimum is 2.9 plate appearances per team game. I am aware that this is not the conventional minimum to use when calculating leaders, and while I do not think it is the best answer I do believe it is more fair than the conventional cutoffs which reflect the reasonings of their eras. And since this site does not feature conventional leaderboards I hope nobody will be too offended.

Everything on this web site copyright © 2004-2010 Alex Reisner, unless specifically noted.