Testing theories with Bayes factors
Bayes factors are a useful tool for researchers in the behavioural and social sciences, partly because they can provide evidence for no effect relative to the sort of effect expected. By contrast, a non-significant result does not provide evidence for the H0 tested. So, if non-significance does not in itself count against any theory predicting an effect, how could a theory fail a test? Bayes factors provide a measure of evidence from first principles. A severe test is one that is likely to obtain evidence against a theory if it were false; that is, to obtain an extreme Bayes factor against the theory. Bayes factors show why hacking and cherry picking degrade evidence; how to deal with multiple testing situations; and how optional stopping is consistent with severe testing. Further, informed Bayes factors can be used to link theory tightly to how that theory is tested, so that the measured evidence does relate to the theory.