Figure 5: Variable Importance (Picture credit: Original)
The figure 5 used Mean Decrease in Gini, which
measures how much each variable contributes to
reducing the impurity in the decision trees that make
up the model. It is indicated in figure 5 that among all
predictors, Min (minutes played) shows the highest
importance score, exceeding a value of 110. This
suggests that playing time is the most influential
factor in the model’s decision-making process. The
other indispensable variables are the TouAttPen,
PasShoAtt and PasShoCmp with over 100 mean
decreases in Gini. These variables play a critical role
in reducing impurity across decision trees. By
contrast, the Goals and G.SoT appear at the bottom of
the chart, with values below 40.
4 CONCLUSION
Overall, the regression model evaluation results
indicate the Random Forest Regression has better
performance. Although the Random Forest model
slightly outperformed the linear regression model in
terms of predictive accuracy, it also exhibited signs of
overfitting, as evidenced by a high training accuracy
(0.997) and a relatively low testing accuracy (0.521).
By analysing the importance of the variables of the
Random Forest model, the paper identified key
performance metrics that significantly influence
market value. The Min (Minutes played),
TouAttPen(Touches in attacking penalty area) and
PasShoAtt(Passes attempted between 5 and 15 yards)
have a strong positive impact on market value, while
Goals (Goals scored or allowed) and G.SoT (Goals
per Shot on Target) show significant negative effects.
Therefore, the football club may prioritize the key
player who consistently receive substantial playing
time and they can focus on the attack player as they
touch more in attacking penalty area compared with
other player. However, one thing that cannot be
ignored is that the dataset used in this study only
contains one season which means it is difficult to
apply to other time series. Further research could be
implemented in the future, aiming to use different
methods to analyze several seasons to improve the
applicability.
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