Models for which the likelihood function can be evaluated only up to a
parameter-dependent unknown normalising constant, such as Markov random field
models, are used widely in computer science, statistical physics, spatial
statistics, and network analysis. However, Bayesian analysis of these models
using standard Monte Carlo methods is not possible due to the intractability of
their likelihood functions. Several methods that permit exact, or close to
exact, simulation from the posterior distribution have recently been developed.
However, estimating the evidence and Bayes' factors (BFs) for these models
remains challenging in general. This paper describes new random weight
importance sampling and sequential Monte Carlo methods for estimating BFs that
use simulation to circumvent the evaluation of the intractable likelihood, and
compares them to existing methods. In some cases we observe an advantage in the
use of biased weight estimates. An initial investigation into the theoretical
and empirical properties of this class of methods is presented. Some support
for the use of biased estimates is presented, but we advocate caution in the
use of such estimates