Bradley-terry models in R: the bradleyterry2 package

This is a short overview of the r add-on package bradleyterry2,which facilitates the specification and fitting of bradley-terry logit,probit or cauchit models to paircomparison data. included are the standard 'unstructured' bradley-terry model,structured versions in which the parameters are related through a linear predictor to explanatory variables,and the possibility of an order or 'home advantage' effect or other 'contest-specific' effects. model fitting is either by maximum likelihood,by penalized quasi-likelihood (for models which involve a random effect),or by bias-reduced maximum likelihood in which the first-order asymptotic bias of parameter estimates is eliminated. also provided are a simple and efficient approach to handling missing covariate data,and suitably-defined residuals for diagnostic checking of the linear predictor.