  This article introduces the bpcs R package (Bayesian Paired Comparison in
Stan) and the statistical models implemented in the package. This package aims
to facilitate the use of Bayesian models for paired comparison data in
behavioral research. Bayesian analysis of paired comparison data allows
parameter estimation even in conditions where the maximum likelihood does not
exist, allows easy extension of paired comparison models, provide
straightforward interpretation of the results with credible intervals, have
better control of type I error, have more robust evidence towards the null
hypothesis, allows propagation of uncertainties, includes prior information,
and perform well when handling models with many parameters and latent
variables. The bpcs package provides a consistent interface for R users and
several functions to evaluate the posterior distribution of all parameters, to
estimate the posterior distribution of any contest between items, and to obtain
the posterior distribution of the ranks. Three reanalyses of recent studies
that used the frequentist Bradley-Terry model are presented. These reanalyses
are conducted with the Bayesian models of the bpcs package, and all the code
used to fit the models, generate the figures, and the tables are available in
the online appendix.
