Computational advances have facilitated application of various Bayesian methods, including the assessment of evidence in favor of a scientific theory. This is accomplished by calculating a Bayes factor. It is important to recognize, however, that the value of a Bayes factor may be sensitive to the choice of priors on parameters appearing in the competing models. This sensitivity is illustrated and discussed. The Schwarz criterion remains a crude yet useful approximation, but more accurate methods will generally require determination of priors and subjective sensitivity analysis.