This notebook follows the Moneyball analysis from Videos 2 and 3. The goal is to use historical baseball data to build regression models for wins, runs scored, and runs allowed.
baseball <- read.csv("baseball.csv")
str(baseball)
'data.frame': 1232 obs. of 15 variables:
$ Team : chr "ARI" "ATL" "BAL" "BOS" ...
$ League : chr "NL" "NL" "AL" "AL" ...
$ Year : int 2012 2012 2012 2012 2012 2012 2012 2012 2012 2012 ...
$ RS : int 734 700 712 734 613 748 669 667 758 726 ...
$ RA : int 688 600 705 806 759 676 588 845 890 670 ...
$ W : int 81 94 93 69 61 85 97 68 64 88 ...
$ OBP : num 0.328 0.32 0.311 0.315 0.302 0.318 0.315 0.324 0.33 0.335 ...
$ SLG : num 0.418 0.389 0.417 0.415 0.378 0.422 0.411 0.381 0.436 0.422 ...
$ BA : num 0.259 0.247 0.247 0.26 0.24 0.255 0.251 0.251 0.274 0.268 ...
$ Playoffs : int 0 1 1 0 0 0 1 0 0 1 ...
$ RankSeason : int NA 4 5 NA NA NA 2 NA NA 6 ...
$ RankPlayoffs: int NA 5 4 NA NA NA 4 NA NA 2 ...
$ G : int 162 162 162 162 162 162 162 162 162 162 ...
$ OOBP : num 0.317 0.306 0.315 0.331 0.335 0.319 0.305 0.336 0.357 0.314 ...
$ OSLG : num 0.415 0.378 0.403 0.428 0.424 0.405 0.39 0.43 0.47 0.402 ...
The dataset contains team, league, year, runs scored, runs allowed, wins, offensive statistics, playoff information, and opponent statistics.
moneyball <- subset(baseball, Year < 2002)
str(moneyball)
'data.frame': 902 obs. of 15 variables:
$ Team : chr "ANA" "ARI" "ATL" "BAL" ...
$ League : chr "AL" "NL" "NL" "AL" ...
$ Year : int 2001 2001 2001 2001 2001 2001 2001 2001 2001 2001 ...
$ RS : int 691 818 729 687 772 777 798 735 897 923 ...
$ RA : int 730 677 643 829 745 701 795 850 821 906 ...
$ W : int 75 92 88 63 82 88 83 66 91 73 ...
$ OBP : num 0.327 0.341 0.324 0.319 0.334 0.336 0.334 0.324 0.35 0.354 ...
$ SLG : num 0.405 0.442 0.412 0.38 0.439 0.43 0.451 0.419 0.458 0.483 ...
$ BA : num 0.261 0.267 0.26 0.248 0.266 0.261 0.268 0.262 0.278 0.292 ...
$ Playoffs : int 0 1 1 0 0 0 0 0 1 0 ...
$ RankSeason : int NA 5 7 NA NA NA NA NA 6 NA ...
$ RankPlayoffs: int NA 1 3 NA NA NA NA NA 4 NA ...
$ G : int 162 162 162 162 161 162 162 162 162 162 ...
$ OOBP : num 0.331 0.311 0.314 0.337 0.329 0.321 0.334 0.341 0.341 0.35 ...
$ OSLG : num 0.412 0.404 0.384 0.439 0.393 0.398 0.427 0.455 0.417 0.48 ...
This keeps only seasons before 2002, which are the seasons used in the Moneyball analysis.
Run difference is calculated as runs scored minus runs allowed.
moneyball$RD <- moneyball$RS - moneyball$RA
str(moneyball)
'data.frame': 902 obs. of 16 variables:
$ Team : chr "ANA" "ARI" "ATL" "BAL" ...
$ League : chr "AL" "NL" "NL" "AL" ...
$ Year : int 2001 2001 2001 2001 2001 2001 2001 2001 2001 2001 ...
$ RS : int 691 818 729 687 772 777 798 735 897 923 ...
$ RA : int 730 677 643 829 745 701 795 850 821 906 ...
$ W : int 75 92 88 63 82 88 83 66 91 73 ...
$ OBP : num 0.327 0.341 0.324 0.319 0.334 0.336 0.334 0.324 0.35 0.354 ...
$ SLG : num 0.405 0.442 0.412 0.38 0.439 0.43 0.451 0.419 0.458 0.483 ...
$ BA : num 0.261 0.267 0.26 0.248 0.266 0.261 0.268 0.262 0.278 0.292 ...
$ Playoffs : int 0 1 1 0 0 0 0 0 1 0 ...
$ RankSeason : int NA 5 7 NA NA NA NA NA 6 NA ...
$ RankPlayoffs: int NA 1 3 NA NA NA NA NA 4 NA ...
$ G : int 162 162 162 162 161 162 162 162 162 162 ...
$ OOBP : num 0.331 0.311 0.314 0.337 0.329 0.321 0.334 0.341 0.341 0.35 ...
$ OSLG : num 0.412 0.404 0.384 0.439 0.393 0.398 0.427 0.455 0.417 0.48 ...
$ RD : int -39 141 86 -142 27 76 3 -115 76 17 ...
A positive run difference means a team scored more runs than it allowed.
plot(
moneyball$RD,
moneyball$W,
xlab = "Run Difference",
ylab = "Wins",
main = "Run Difference and Team Wins"
)
The scatterplot should show a strong positive linear relationship.
WinsReg <- lm(W ~ RD, data = moneyball)
summary(WinsReg)
Call:
lm(formula = W ~ RD, data = moneyball)
Residuals:
Min 1Q Median 3Q Max
-14.2662 -2.6509 0.1234 2.9364 11.6570
Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) 80.881375 0.131157 616.67 <2e-16 ***
RD 0.105766 0.001297 81.55 <2e-16 ***
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
Residual standard error: 3.939 on 900 degrees of freedom
Multiple R-squared: 0.8808, Adjusted R-squared: 0.8807
F-statistic: 6651 on 1 and 900 DF, p-value: < 2.2e-16
The estimated equation is approximately:
\[ \widehat{W} = 80.88 + 0.106(RD) \]
This means about 9 to 10 additional runs of run difference are associated with one extra win. The model explains about 88.1% of the variation in wins.
RunsReg_full <- lm(RS ~ OBP + SLG + BA, data = moneyball)
summary(RunsReg_full)
Call:
lm(formula = RS ~ OBP + SLG + BA, data = moneyball)
Residuals:
Min 1Q Median 3Q Max
-70.941 -17.247 -0.621 16.754 90.998
Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) -788.46 19.70 -40.029 < 2e-16 ***
OBP 2917.42 110.47 26.410 < 2e-16 ***
SLG 1637.93 45.99 35.612 < 2e-16 ***
BA -368.97 130.58 -2.826 0.00482 **
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
Residual standard error: 24.69 on 898 degrees of freedom
Multiple R-squared: 0.9302, Adjusted R-squared: 0.93
F-statistic: 3989 on 3 and 898 DF, p-value: < 2.2e-16
This model explains about 93% of the variation in runs scored. OBP and SLG are strong positive predictors.
RunsReg <- lm(RS ~ OBP + SLG, data = moneyball)
summary(RunsReg)
Call:
lm(formula = RS ~ OBP + SLG, data = moneyball)
Residuals:
Min 1Q Median 3Q Max
-70.838 -17.174 -1.108 16.770 90.036
Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) -804.63 18.92 -42.53 <2e-16 ***
OBP 2737.77 90.68 30.19 <2e-16 ***
SLG 1584.91 42.16 37.60 <2e-16 ***
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
Residual standard error: 24.79 on 899 degrees of freedom
Multiple R-squared: 0.9296, Adjusted R-squared: 0.9294
F-statistic: 5934 on 2 and 899 DF, p-value: < 2.2e-16
The reduced model is approximately:
\[ \widehat{RS} = -804.63 + 2737.77(OBP) + 1584.91(SLG) \]
The R-squared remains about 0.930, so removing batting average creates a simpler model with nearly the same performance.
Higher OBP and SLG are associated with more runs scored. Both predictors are statistically significant, and together they explain about 92.96% of the variation in runs scored.
RunsAllowedReg <- lm(RA ~ OOBP + OSLG, data = moneyball)
summary(RunsAllowedReg)
Call:
lm(formula = RA ~ OOBP + OSLG, data = moneyball)
Residuals:
Min 1Q Median 3Q Max
-82.397 -15.178 -0.129 17.679 60.955
Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) -837.38 60.26 -13.897 < 2e-16 ***
OOBP 2913.60 291.97 9.979 4.46e-16 ***
OSLG 1514.29 175.43 8.632 2.55e-13 ***
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
Residual standard error: 25.67 on 87 degrees of freedom
(812 observations deleted due to missingness)
Multiple R-squared: 0.9073, Adjusted R-squared: 0.9052
F-statistic: 425.8 on 2 and 87 DF, p-value: < 2.2e-16
The estimated model is approximately:
\[ \widehat{RA} = -837.38 + 2913.60(OOBP) + 1514.29(OSLG) \]
Higher opponent OBP and opponent SLG are associated with more runs allowed. The model explains about 90.7% of the variation in runs allowed for the observations used.
sum(is.na(moneyball$OOBP))
[1] 812
sum(is.na(moneyball$OSLG))
[1] 812
Many rows have missing values for OOBP or OSLG. R automatically removes those rows when fitting the runs-allowed model.
summary(WinsReg)
Call:
lm(formula = W ~ RD, data = moneyball)
Residuals:
Min 1Q Median 3Q Max
-14.2662 -2.6509 0.1234 2.9364 11.6570
Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) 80.881375 0.131157 616.67 <2e-16 ***
RD 0.105766 0.001297 81.55 <2e-16 ***
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
Residual standard error: 3.939 on 900 degrees of freedom
Multiple R-squared: 0.8808, Adjusted R-squared: 0.8807
F-statistic: 6651 on 1 and 900 DF, p-value: < 2.2e-16
summary(RunsReg)
Call:
lm(formula = RS ~ OBP + SLG, data = moneyball)
Residuals:
Min 1Q Median 3Q Max
-70.838 -17.174 -1.108 16.770 90.036
Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) -804.63 18.92 -42.53 <2e-16 ***
OBP 2737.77 90.68 30.19 <2e-16 ***
SLG 1584.91 42.16 37.60 <2e-16 ***
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
Residual standard error: 24.79 on 899 degrees of freedom
Multiple R-squared: 0.9296, Adjusted R-squared: 0.9294
F-statistic: 5934 on 2 and 899 DF, p-value: < 2.2e-16
summary(RunsAllowedReg)
Call:
lm(formula = RA ~ OOBP + OSLG, data = moneyball)
Residuals:
Min 1Q Median 3Q Max
-82.397 -15.178 -0.129 17.679 60.955
Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) -837.38 60.26 -13.897 < 2e-16 ***
OOBP 2913.60 291.97 9.979 4.46e-16 ***
OSLG 1514.29 175.43 8.632 2.55e-13 ***
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
Residual standard error: 25.67 on 87 degrees of freedom
(812 observations deleted due to missingness)
Multiple R-squared: 0.9073, Adjusted R-squared: 0.9052
F-statistic: 425.8 on 2 and 87 DF, p-value: < 2.2e-16
Approximate R-squared values:
All three models show strong relationships.
The analysis shows that run difference is a strong predictor of wins. OBP and SLG are strong predictors of runs scored, while opponent OBP and opponent SLG are strong predictors of runs allowed. These results support the use of statistical analysis in baseball decision-making.