BTdecayLassoF {BTdecayLasso}R Documentation

Bradley-Terry Model with Exponential Decayed weighted likelihood and Adaptive Lasso with a given penalty rate

Description

This function provides a method to computed the estimated abilities and lambda given an intuitive fixed Lasso penalty rate. Since in Lasso method, the selection of lambda varies a lot with respect to different datasets. We can keep the consistency of amount of Lasso penalty induced in different datasets from different period by setting a fixed Lasso penalty rate "penalty". Please refer to BTdecayLasso for the definition of "penalty" and its relationship with "lambda".

Usage

BTdecayLassoF(dataframe, ability, penalty, decay.rate = 0, fixed = 1,
  thersh = 1e-05, max = 100, iter = 100)

Arguments

dataframe

Generated using BTdataframe given raw data.

ability

A column vector of teams ability, the last row is the home parameter. It can be generated using BTdataframe given raw data. The row number is consistent with the team's index shown in dataframe. It can be generated using BTdataframe given raw data.

penalty

The amount of Lasso penalty induced (1-s/max(s)) where is the sum of Lasso penalty part.

decay.rate

The exponential decay rate. Usually ranging from (0, 0.01), A larger decay rate weights more importance to most recent matches and the estimated parameters reflect more on recent behaviour.

fixed

A teams index whose ability will be fixed as 0. The worstTeam's index can be generated using BTdataframe given raw data.

thersh

Threshold for convergence

max

Maximum weight for w_ij (weight used for Adaptive Lasso)

iter

Number of iterations used in L-BFGS-B algorithm.

Details

The estimated ability given fixed penalty p = 1- s/\max(s) where s is the sum of Lasso penalty part. When p = 0, this model is reduced to a standard Bradley-Terry Model. When p = 1, all ability scores are shrinking to 0.

The parameter "penalty" should be ranging from 0.01 to 0.99 due to the iteration's convergent error.

summary() function can be applied to view the outputs.

Value

The list with class "BTF" contains estimated abilities and other parameters.

ability

Estimated ability scores

df

Degree of freedom (number of distinct μ)

penalty

Amount of Lasso Penalty

decay.rate

Exponential decay rate

lambda

Corresponding Lasso lambda given penalty rate

References

Masarotto, G. and Varin, C.(2012) The Ranking Lasso and its Application to Sport Tournaments. *The Annals of Applied Statistics* **6** 1949–1970.

Zou, H. (2006) The adaptive lasso and its oracle properties. *J.Amer.Statist.Assoc* **101** 1418–1429.

See Also

BTdataframe for dataframe initialization, BTdecayLasso for detailed description

Examples

##Initializing Dataframe
x <- BTdataframe(NFL2010)

##The following code runs the main results

##BTdecayLasso run with exponential decay rate 0.005 and Lasso penaty 0.5
y <- BTdecayLassoF(x$dataframe, x$ability, 0.5, decay.rate = 0.005, 
                   fixed = x$worstTeam)
summary(y)



[Package BTdecayLasso version 0.1.0 Index]