Mike Gershman and Pete Palmer of Total Sports, two of the authors of Total Baseball: The Official Encyclopedia of Major League Baseball, helped devise the Baseball Time Machine (to learn about the Exploratorium's role, see our credits page). This page provides answers to frequently asked questions about the Time Machine, as well the original formula used to devise the numbers. Definitions of some of the statistical terms used here are at the bottom of this page.

How was the Time Machine calculation devised?

"First, I started with a file of the complete lifetime data for every player. I just extracted the information on the player I was interested in, and then I calculated the average for each year for each league. I added up the averages of each player, omitted the pitchers, and then came up with an average figure.

Then I took the player in question and figured out how he related to the league average for the years he played. When I moved him to a different era, I maintained that relationship. For example, if he was 10% above the league average in 1920 -- say the average was .290 and he hit .320 --then, if I moved him to 1963 and the league average was .240, his average would be 10% higher, which would be .264. It's really just as simple as that.

The other thing I did was to take into account the number of games scheduled. For instance, when Babe Ruth played, they had 154 games. Now they have 162. So that gives Babe Ruth about a 5% edge in games played if you moved him forward in time. Now, if you go back to Dan Brouthers in the 19th century, when they used to play 80 or 90 games (they didn't actually get up over 154 until 1904, I believe), that gives Brouthers an advantage in playing more games if you move him forward in time."

What about the home run figures?

"The problem with normalizing home runs is that Ruth was so far ahead of anyone else in his day. He out-homered almost every other team (in yearly totals). There was really nobody in the same class with him at all. So I normalized batting average, on-base average, and slugging average. In slugging average, it's total bases per at-bat. If you normalize the total bases and then distribute them among doubles, triples, and home runs, you get a more reasonable number of home runs. Then Babe Ruth would get 80 or 90 in a season, not 200."

What factors are not included?

"I didn't take into account any ballpark effects. So the average for the league is for all ballparks. Whatever advantage or disadvantage a player had playing in their home ballpark in the particular years they played is carried over.

Also, I assumed that an average player in any given year was equally good. You could make an argument that today's players are better. Even though the expansion has increased the number of teams from 16 to 30, it hasn't kept pace with U.S. population growth. We also have a lot more foreign players, especially from the Dominican Republic, but also the rest of the Caribbean. We have players from Australia, Japan, and Korea. Plus, of course, until Jackie Robinson came along, we had no African-American players in major leagues. So the pool of players available to the major leagues is much greater now than the increase in the number of teams. But, for this exercise, I just assumed that an average player from 1876 was as good as an average player from 1998."


Want to try the calculation yourself?

To see the formula, league averages for every year from 1871 to 1995, and the original stats for Willie Mays, Hank Aaron, and Mark McGwire, click here.

Definitions of Statistical Terms
(Some of the information here is from Total Baseball: The Official Encyclopedia of Major League Baseball.)


2B -- Doubles

3B -- Triples

AB -- At-Bats

AVG -- Batting Average

BB -- Bases on Balls

G -- Games played

H -- Hits

HR -- Home Runs. When is a home run not a home run? Before 1920, not if it came with men on base in the ultimate inning and created a margin of victory greater than one run. A ruling of Special Baseball Records Committee in 1969 reversed its earlier decision that had made home runs of 37 disputed final-inning, game-winning base hits. In accordance with the practice of the day, such a hit, even if it sailed out of the park, would be credited with only as many bases as necessary to plate the winning run. Thus Babe Ruth's "715th home run," hit on July 8, 1918, to win a game against Cleveland, remained a triple.

L -- League, either American or National

Normalizing -- Restating a figure as a ratio by comparing it to the leaque average or norm.

On Base Percentage -- Hits plus walks plus hit by pitch, divided by at-bats plus walks plus hit by pitch.

Production -- On Base Percentage plus Slugging Average; a simple but elegant measure of batting prowess, in that the weakness of one-half of the formulation, On Base Percentage iscountered by the strength of the other, Slugging Average, and vice versa.

R -- Runs Scored

RBI -- Runs Batted In

SB -- Stolen Bases

Slugging Average -- Total bases divided by at-bats; combines nicely with On Base Percentage to create Production.

TB -- Total Bases

YEARS --The years in which the player originally played and the years that you've selected using the "Time Machine."