  We look at the distribution of the Bayesian evidence for mock realizations of
supernova and baryon acoustic oscillation data. The ratios of Bayesian
evidences of different models are often used to perform model selection. The
significance of these Bayes factors are then interpreted using scales such as
the Jeffreys or Kass \& Raftery scale. First, we demonstrate how to use the
evidence itself to validate the model, that is to say how well a model fits the
data, regardless of how well other models perform. The basic idea is that if,
for some real dataset a model's evidence lies outside the distribution of
evidences that result when the same fiducial model that generates the datasets
is used for the analysis, then the model in question is robustly ruled out.
Further, we show how to assess the significance of a hypothetically computed
Bayes factor. We show that the range of the distribution of Bayes factors can
greatly depend on the models in question and also the number of data points in
the dataset. Thus, we have demonstrated that the significance of Bayes factors
needs to be calculated for each unique dataset.
