BBTm.no.formula {speedyBBT}R Documentation

Bayesian Bradley–Terry model with comparison specific effect

Description

This function fits the Bradley-Terry model with a comparison specific effect. Each comparison can be assigned a real value to allow for a specific effect for the comparison, such as bias, ordering or home/away effect. The value of this effect is denoted $kappa$. The function places a normal prior distribution on both kappa and the player quality parameters lambda.

Usage

BBTm.no.formula(
  outcome,
  player1,
  player2,
  player.prior.var,
  lambda.initial,
  advantage = NULL,
  kappa.initial = NULL,
  kappa.var = NULL,
  n.iter = 1000,
  hyperparameter = TRUE,
  chi = 0.01,
  psi = 0.01
)

Arguments

outcome

vector of outcomes. 1 if player2 is the winner, 0 if player1 is the winner

player1

vector of first players.

player2

vector of second players.

player.prior.var

(optional) matrix specifying the prior covariance of the player correlation parameters

lambda.initial

(optional) vector containing the values of the player parameters for the first MCMC iteration

advantage

(optional) a vector with the value of the comparisons specific effect for each comparison

kappa.initial

(optional) an initial value for the comparison specific value kappa @param kappa.var (optional) the prior variance of the he comparison specific value kappa

n.iter

number of MCMC samples to be drawn

hyperparameter

boolean indicating if inference should be performed for the prior variance hyperparameter. If TRUE the prior variance (main diagonal of the covariance matrix) must be set to 1.

chi

rate parameter for the inverse-gamma prior distribution on the hyperparameter

psi

shape parameter for the inverse-gamma prior distribution on the hyperparameter

Details

If player.prior.var is omitted, independent and identical N(0, 5^2) prior distributions are placed on each object quality parameter.

If lambda.initial is omitted, it is set to a vector of zeroes.

If lambda.var is omitted, it is set to N(0, 5^2).

Value

A data frame containing samples from the posterior distribution


[Package speedyBBT version 1.0 Index]