A Comparison of Covariate-based Predictition Methods for FIFA World Cups A. Groll Faculty of Statistics, TU Dortmund University (joint work with J. Abedieh, C. Ley, A. Mayr, T. Kneib, G. Schauberger, G. Tutz & H. Van Eetvelde) Zurich R User Group Meetup October 25 th 2018, University of Zurich A. Groll (TU Dortmund) Predicting International Soccer Tournaments 1 / 38
Who will celebrate? Sources: youtube.com,EMAJ Magazine,youfrisky.com,Bailiwick Express A. Groll (TU Dortmund) Predicting International Soccer Tournaments 2 / 38
Who will cry? Sources: youtube.com,pinterest,BBC,Daily Mail A. Groll (TU Dortmund) Predicting International Soccer Tournaments 3 / 38
Theoretical Background A. Groll (TU Dortmund) Predicting International Soccer Tournaments 4 / 38
Part I: Regression-based Methods A. Groll (TU Dortmund) Predicting International Soccer Tournaments 5 / 38
Model for international soccer tournaments y ijk ∣ x ik , x jk ∼ Pois ( λ ijk ) i , j ∈ { 1 ,..., n } , i ≠ j λ ijk = exp ( β 0 + ( x ik − x jk ) ⊺ β ) n : Number of teams y ijk : Number of goals scored by team i against opponent j at tournament k x ik , x jk : Covariate vectors of team i and opponent j varying over tournaments β : Parameter vector of covariate effects A. Groll (TU Dortmund) Predicting International Soccer Tournaments 6 / 38
Regularized estimation Maximize penalized log-likelihood l p ( β 0 ,β β ) = l ( β 0 ,β β ) − λ J ( β β ) β β β A. Groll (TU Dortmund) Predicting International Soccer Tournaments 7 / 38
Regularized estimation Maximize penalized log-likelihood l p ( β 0 ,β β ) = l ( β 0 ,β β ) − λ J ( β β ) β β β = l ( β 0 ,β β ) − λ p ∣ β i ∣ , ∑ β i = 1 with lasso penalty term (Tibshirani, 1996): p J ( β β ) = ∣ β i ∣ . ∑ β i = 1 The model can be estimated with the R -package glmnet (Friedman et al., 2010). A. Groll (TU Dortmund) Predicting International Soccer Tournaments 7 / 38
Regularized estimation Maximize penalized log-likelihood l p ( β 0 ,β β ) = l ( β 0 ,β β ) − λ J ( β β ) β β β = l ( β 0 ,β β ) − λ p ∣ β i ∣ , ∑ β i = 1 with lasso penalty term (Tibshirani, 1996): p J ( β β ) = ∣ β i ∣ . ∑ β i = 1 The model can be estimated with the R -package glmnet (Friedman et al., 2010). Versions used for: EURO 2012 (Groll and Abedieh, 2013); World Cup 2014 (Groll et al., 2015); EURO 2016 (Groll et al., 2018) A. Groll (TU Dortmund) Predicting International Soccer Tournaments 7 / 38
Part II: Ranking Methods A. Groll (TU Dortmund) Predicting International Soccer Tournaments 8 / 38
Independent Poisson ranking model ∼ Pois ( λ ijm ) , Y ijm = exp ( β 0 + ( r i − r j ) + h ⋅ I ( team i playing at home )) λ ijm n : Number of teams M : Number of matches y ijm : Number of goals scored by team i against opponent j in match m r i , r j : strengths / ability parameters of team i and team j h : home effect; added if team i plays at home A. Groll (TU Dortmund) Predicting International Soccer Tournaments 9 / 38
Independent Poisson ranking model Likelihood function : ⎛ y jim ! exp ( − λ jim )⎞ w type , m ⋅ w time , m λ y ijm λ y jim L = ∏ M y ijm ! exp (− λ ijm ) ⋅ ijm jim ⎝ ⎠ , m = 1 with weights tm w time , m ( t m ) = ( 1 2 ) Half period and w type , m ∈ { 1 , 2 , 3 , 4 } (depending on type of match) . A. Groll (TU Dortmund) Predicting International Soccer Tournaments 10 / 38
Independent Poisson ranking model Likelihood function : ⎛ y jim ! exp (− λ jim )⎞ w type , m ⋅ w time , m λ y ijm λ y jim L = M y ijm ! exp (− λ ijm ) ⋅ ∏ ijm jim , ⎝ ⎠ m = 1 with weights tm w time , m ( t m ) = ( 1 2 ) Half period and w type , m ∈ { 1 , 2 , 3 , 4 } (depending on type of match) . Different extensions, for example, bivariate Poisson models . Ley et al. (2018) show that bivariate Poisson with Half Period of 3 years is best for prediction. A. Groll (TU Dortmund) Predicting International Soccer Tournaments 10 / 38
Part III: Random Forests A. Groll (TU Dortmund) Predicting International Soccer Tournaments 11 / 38
Random Forests ● introduced by Breiman (2001) ● principle : aggregation of (large) number of classification / regression trees � ⇒ can be used both for classification & regression purposes A. Groll (TU Dortmund) Predicting International Soccer Tournaments 12 / 38
Random Forests ● introduced by Breiman (2001) ● principle : aggregation of (large) number of classification / regression trees � ⇒ can be used both for classification & regression purposes ● final predictions : single tree predictions are aggregated, either by majority vote (classification) or by averaging (regression) A. Groll (TU Dortmund) Predicting International Soccer Tournaments 12 / 38
Random Forests ● introduced by Breiman (2001) ● principle : aggregation of (large) number of classification / regression trees � ⇒ can be used both for classification & regression purposes ● final predictions : single tree predictions are aggregated, either by majority vote (classification) or by averaging (regression) ● feature space is partitioned recursively, each partition has its own prediction A. Groll (TU Dortmund) Predicting International Soccer Tournaments 12 / 38
Random Forests ● introduced by Breiman (2001) ● principle : aggregation of (large) number of classification / regression trees � ⇒ can be used both for classification & regression purposes ● final predictions : single tree predictions are aggregated, either by majority vote (classification) or by averaging (regression) ● feature space is partitioned recursively, each partition has its own prediction ● find split with strongest difference between the two new partitions w.r.t. some criterion A. Groll (TU Dortmund) Predicting International Soccer Tournaments 12 / 38
Random Forests ● introduced by Breiman (2001) ● principle : aggregation of (large) number of classification / regression trees � ⇒ can be used both for classification & regression purposes ● final predictions : single tree predictions are aggregated, either by majority vote (classification) or by averaging (regression) ● feature space is partitioned recursively, each partition has its own prediction ● find split with strongest difference between the two new partitions w.r.t. some criterion ● Observations within the same partition as similar as possible, observations from different partitions very different (w.r.t. response variable) A. Groll (TU Dortmund) Predicting International Soccer Tournaments 12 / 38
Random Forests ● introduced by Breiman (2001) ● principle : aggregation of (large) number of classification / regression trees � ⇒ can be used both for classification & regression purposes ● final predictions : single tree predictions are aggregated, either by majority vote (classification) or by averaging (regression) ● feature space is partitioned recursively, each partition has its own prediction ● find split with strongest difference between the two new partitions w.r.t. some criterion ● Observations within the same partition as similar as possible, observations from different partitions very different (w.r.t. response variable) ● a single tree is usually pruned (lower variance but increases bias) A. Groll (TU Dortmund) Predicting International Soccer Tournaments 12 / 38
Random Forests ● introduced by Breiman (2001) ● principle : aggregation of (large) number of classification / regression trees � ⇒ can be used both for classification & regression purposes ● final predictions : single tree predictions are aggregated, either by majority vote (classification) or by averaging (regression) ● feature space is partitioned recursively, each partition has its own prediction ● find split with strongest difference between the two new partitions w.r.t. some criterion ● Observations within the same partition as similar as possible, observations from different partitions very different (w.r.t. response variable) ● a single tree is usually pruned (lower variance but increases bias) ● visualized in dendrogram A. Groll (TU Dortmund) Predicting International Soccer Tournaments 12 / 38
Dendrogram of regression tree 1 Rank p < 0.001 ≤ −15 > −15 3 Oddset p = 0.003 ≤ −0.003 > −0.003 Node 2 (n = 139) Node 4 (n = 213) Node 5 (n = 160) 8 8 8 6 6 6 4 4 4 2 2 2 0 0 0 Exemplary regression tree for FIFA World Cup 2002 – 2014 data using the function ctree from the R -package party (Hothorn et al., 2006). Response : Number of goals ; predictors : only FIFA Rank and Oddset are used. A. Groll (TU Dortmund) Predicting International Soccer Tournaments 13 / 38
Random Forests ● repeatedly grow different regression trees ● main goal: decrease variance A. Groll (TU Dortmund) Predicting International Soccer Tournaments 14 / 38
Random Forests ● repeatedly grow different regression trees ● main goal: decrease variance � ⇒ decrease correlation between single trees. A. Groll (TU Dortmund) Predicting International Soccer Tournaments 14 / 38
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