基礎知識

年齢曲線



年齢曲線(Aging Curve)とは、選手のパフォーマンスが年齢にしたがってどう変化していくかの傾向をいう。年齢を横軸、パフォーマンスの高さを縦軸にとってグラフを描くと一般的に若いうちは年齢とともに能力が上昇していきある一定の年齢を超えると下降していく放物線のような形の曲線となることから年齢曲線という呼び名がある。


統計データから年齢曲線を描くのは複雑なプロセスであり、研究者によって手法は異なる。まず、単に全選手の成績を年齢別に集計するだけでは能力の異なる選手同士の比較になってしまい、年齢の違いだけによる成績の差を抽出できない。そこで2つの連続する年(例えば2016年と2017年)で出場した選手のデータを集め、前後の変化だけを集計していき一般的な傾向を探るという操作が必要になる。その他年齢の要素のみを抽出するため各種の補正が行われる。


上記の都合により参照する研究によって細部は異なるが、大まかな結論は概ね次の通りである。まず、打者に関してはwOBAのような打撃指標を対象としてデータをとると27歳が最もパフォーマンスが高い年齢であるという結論になることが多い。守備についてはもう少し若い年齢がピークであるとする説が多く、遊撃手について23~28歳をピーク年齢と推定した研究がある。


投手に関しては野手のような年齢曲線が描かれず、若いうちから年齢を重ねるほどにパフォーマンスが低下していくという結果が示されることが多い。これに関しては実際に投手は消耗品的な側面が強いためデータが正しいとする見解と、統計処理上の問題であり適切な補正を加えればもう少し野手に近い曲線が描かれるはずだとする見解がある。



参考サイト

How do baseball players age? (Part 1)
How do baseball players age? (Part 2)
Fielding aging curves
How Do Pitchers Age?

参考文献


「年齢の変化と成績の関係」(岡田友輔他『セイバーメトリクス・リポート1』水曜社2012)


指標一覧

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1B
One-base Hit
Batting > Standard
2B
Two-base Hit
Batting > Standard
3B
Three-base Hit
Batting > Standard
AVG
Batting Average
Batting > Standard
AVG
Batting Average
Batting > Advanced
AVG
hits allowed average
Pitching > Advanced
BABIP
Batting Average on Balls In Play
Batting > Advanced
BB
Base on Ball
Batting > Standard
BB
walks and given
Pitching > Standard
BB/K
walk-to-strikeout ratio
Batting > Advanced
BUH%
bunt hit percentage
Batting > Batted Ball
CG
complete game
Pitching > Standard
CS
Caught Stealing
Batting > Standard
CS
caught stealing
Pitching > Standard
ERA
earned run average
Pitching > Standard
exLI
Average Leverage Index when exiting the game
Pitching > Win Probability
FB%
fly ball percentage
Batting > Batted Ball
FB%
fly ball percentage
Pitching > Batted Ball
FT%
Two Seam Fastball percentage
Batting > Pitch Type
FT%
Two Seam Fastball percentage
Pitching > Pitch Type
FTv
Two Seam Fastball velocity
Batting > Pitch Type
FTv
Two Seam Fastball velocity
Pitching > Pitch Type
GB%
ground ball percentage
Batting > Batted Ball
GB%
ground ball percentage
Pitching > Batted Ball
GB/FB
ground ball to fly ball ratio
Batting > Batted Ball
GB/FB
ground ball to fly ball ratio
Pitching > Batted Ball
GBOut%
ground ball out percentage
Batting > Batted Ball
GDP
Grounded into Double Play
Batting > Standard
gmLI
Average Leverage Index when entering the game
Pitching > Win Probability
HBP
Hit By Pitch
Batting > Standard
HBP
hit by pitch
Pitching > Standard
HR
home runs allowed
Pitching > Standard
IBB
Intentional Base on Ball
Batting > Standard
IBB
intentional base on balls
Pitching > Standard
IFFB%
infield fly ball percentage
Batting > Batted Ball
IFFB%
infield fly ball percentage
Pitching > Batted Ball
IFH%
infield hit percentage
Batting > Batted Ball
inLI
Average Leverage Index at the start of the inning
Pitching > Win Probability
IP
innings pitched
Pitching > Standard
K%
strikeouts rate
Batting > Advanced
K-BB%
strikeout-walk rate differential
Pitching > Advanced
LD%
line drive percentage
Batting > Batted Ball
LD%
line drive percentage
Pitching > Batted Ball
OBP
On-Base Percentage
Batting > Advanced
O-Contact%
Z-Contact%
Contact%
contact percentage
Batting > Plate Discipline
O-Contact%
Z-Contact%
Contact%
contact percentage
Pitching > Plate Discipline
OFOut%
outfield fly out percentage
Batting > Batted Ball
OPS
On-base Plus Slugging percentage
Batting > Advanced
O-Swing%
Z-Swing%
Swing%
SwStr%
swing percentage
Batting > Plate Discipline
O-Swing%
Z-Swing%
Swing%
SwStr%
swing percentage
Pitching > Plate Discipline
PA
Plate Appearance
Batting > Standard
PH
Pinch Hit Opportunities
Batting > Win Probability
PhLI
Average Leverage Index while Pinch Hitting
Batting > Win Probability
pLI
Player Average Leverage Index
Batting > Win Probability
pLI
Player Average Leverage Index
Pitching > Win Probability
Pull%
Cent%
Oppo%
batted ball direction
Batting > Batted Ball
Pull%
Cent%
Oppo%
batted ball direction
Pitching > Batted Ball
R
runs allowed
Pitching > Standard
RBI
Runs Batted In
Batting > Standard
RE24
Run Above Average based on the 24 Base/Out States
Batting > Win Probability
RE24
Run Above Average based on the 24 Base/Out States
Pitching > Win Probability
REW
Wins Above Average based on the 24 Base/Out States
Batting > Win Probability
REW
Wins Above Average based on the 24 Base/Out States
Pitching > Win Probability
SB
Steal a Base
Batting > Standard
SB
steal a base
Pitching > Standard
SF
Sacrifice Fly
Batting > Standard
SH
Sacrifice Hit
Batting > Standard
SLG
Slugging percentage
Batting > Advanced
SO
Strike Out
Batting > Standard
Soft%
Mid%
Hard%
quality of contact stats
Batting > Batted Ball
Soft%
Mid%
Hard%
quality of contact stats
Pitching > Batted Ball
TBF
total batters faced
Pitching > Standard
WAR
wins above replacement
Batting > Value
WAR
WAR
wins above replacement
Pitching > Value
WAR
wCB/C
Curveball runs above average per 100 pitches
Batting > Pitch Value
wCB/C
Curveball runs above average per 100 pitches
Pitching > Pitch Value
wCH/C
Changeup runs above average per 100 pitches
Pitching > Pitch Value
wCT/C
Cutter runs above average per 100 pitches
Pitching > Pitch Value
wFA/C
Fastball runs above average per 100 pitches
Batting > Pitch Value
wFA/C
Fastball runs above average per 100 pitches
Pitching > Pitch Value
wFT
Two Seam Fastball runs above average
Batting > Pitch Value
wFT
Two Seam Fastball runs above average
Pitching > Pitch Value
wFT/C
Two Seam Fastball runs above average per 100 pitches
Batting > Pitch Value
wFT/C
Two Seam Fastball runs above average per 100 pitches
Pitching > Pitch Value
WP
wild pitch
Pitching > Standard
wSB
weighted Stolen Base runs
Batting > Advanced
wSF/C
Splitter runs above average per 100 pitches
Batting > Pitch Value
wSF/C
Splitter runs above average per 100 pitches
Pitching > Pitch Value
wSI/C
Sinker runs above average per 100 pitches
Batting > Pitch Value
wSI/C
Sinker runs above average per 100 pitches
Pitching > Pitch Value
wSL/C
Slider runs above average per 100 pitches
Batting > Pitch Value
wSL/C
Slider runs above average per 100 pitches
Pitching > Pitch Value
wSP/C
Special runs above average per 100 pitches
Batting > Pitch Value
wSP/C
Special runs above average per 100 pitches
Pitching > Pitch Value
Zone%
F-Strike%
pitches in the strike zone percentage
Batting > Plate Discipline
Zone%
F-Strike%
pitches in the strike zone percentage
Pitching > Plate Discipline
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