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Wednesday, September 2, 2015

Age can be misleading at baseball-reference.com

baseball-reference.com does a great job.  It's my favorite website for baseball data.  I recently used its "player index" (ad hoc query) function to create lists of players sorted by age:

50 homers sorted by age Wednesday, September 2, 2015

30 homers, age 22 or younger Wednesday, September 2, 2015

30 homers, age 37 and older Tuesday, September 1, 2015

Age is determined before July 1.  So Alex Rodriguez is considered 39 by baseball-reference.com even though he turned 40 in July.,,

Darrell Evans is the only 40 year old to hit at least 30 homers: 34 in 1987.
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That conclusion that I reached regarding Evans may not be correct, depending on the birthdays of players who were still 39 on June 30 of the year in which they reached 30 homers in a season.  baseball-reference.com does its calculation of age based on age at mid season but the actual accomplishment may occur in the second half of the season.  For season home run totals it almost always will.

Hank Aaron hit 40 homers in 1973 and list as being 39 years old.  Hank's birthday was Feb. 5, 1934 so his integer age will be the same for all of the 1973 season.  baseball-reference.com appears to calculate the age for living players based on today's date and the players's birthday.  Aaron is listed as Age 81.209.

Barry Bonds is listed in the query results as being 39 in 2004 when he hit 45 home runs:
Born: July 241964 in Riverside, CA (Age 51.040)

Clearly on planet earth Bonds would be considered 40 years old by the time he hit homer 30 in 2004.  Bonds home run log:

http://www.baseball-reference.com/players/event_hr.cgi?id=bondsba01&t=b

shows that Bonds hit #30:

Tuesday, August 10, 2004, 7:05PM, PNC Park
Attendance: 24,930, Time of Game: 2:55
Pirates 8, Giants 7

HR: Barry Bonds (30, off John Grabow, 7th inn, 0 on, 0 outs to CF-RF)


Tech Note: To compute age I used Google Docs Sheets function yearfrac, which resulted in a slightly different age for Bonds today: 51.105.  Maybe baseball-reference.com figures ages at the beginning of the week, not each day.

On August 10, 2004 the age of Barry Bonds would have been 40.044.  Even later in 2004 Bonds would hit number 40 off Jamey Wright on Sept. 7, 2004 at age 40.119.  So we could say that Barry Bonds hit 40 homers at the age of 40.  Not all 40 homers but then that same applies to any player whose birthday occurs during the season.

This is a bit narrow but even what baseball-reference.com presents in its lists when sorted by age can be misleading.  It seems that baseball-reference.com sorts age by the integer so that the order of multiple players with the same integer age is random.  Let's look at three 34 year old players who hit at least 50 homers in a season.  They are in the list in my post earlier today on that subject:


3Johnny Mize51194734NYGNL15466458613717726213874424062.302.384.614.998*3
4Mark McGwire70199834STLNL15568150913015221014716228155604810.299.470.7521.222*3/H
5Willie Mays52196534SFGNL1576385581181772131127616710221194.317.398.6451.043*8/H97

Mize:Born: January 71913 in Demorest, GA

Died: June 21993 in Demorest, GA (Aged 80.146)

McGwire: Born: October 11963 in Pomona, CA (Age 51.336) 

Mays: Born: May 61931 in Westfield, AL (Age 84.119) 

Let's figure their ages on June 30 of the year in which they hit at least 50 homers.


born50 HRAge
Mize1/7/19136/30/194734.48055556
McGwire10/1/19636/30/199834.74722222
Mays5/6/19316/30/196534.15

As you can see, baseball-reference.com did not put them in descending order by age when decimal places are considered.  The order should have been: McGwire, Mize, Mays.

Not a super big deal but it does impact the type of stuff that I was addressing.  This can easily be fixed by presenting the decimal places for age when something is accomplished as baseball-reference.com does when showing the player's age either today or at the time of death.

Even if the list generated is not sorted by age, it contains age.  I often wonder about just how old a player is.  Providing the decimal places would show that.  I hope that baseball-reference.com will consider implementing this change.  It would improve an already great website.

Sept. 5, 2015:
baseball-reference.com shows player age as "yy.ddd". Who knew? Saturday, September 5, 2015

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