Bayes to the rescue: Does the type of hypnotic induction matter?

Abstract

Studies comparing different forms of hypnotic induction (e.g., indirect vs. direct induction) on responsiveness to suggestion have typically found no significant difference between induction types. However, no firm conclusion can be drawn from a nonsignificant result. In contrast, Bayes factors (Jeffreys, 1939/1961) indicate whether evidence favors H0 and against the alternative hypothesis or whether data are simply insensitive. Here, we apply Bayes factors to those nonsignificant results to decide: Does the form of hypnotic induction really not matter, does it matter, or should we suspend judgment? As the claim that different inductions are differentially effective comes mostly from clinicians, we based the Bayes factors on hypnotherapists’ judgments of expected differences between inductions. In addition, we also used empirical differences between induction versus no-induction as an estimate of the order of size of effect that could be expected between different inductions, independent of clinical judgment. As a whole, the Bayesian reanalysis of the present evidence supports the claim that additional research should be done on the influence of the induction procedure on hypnotic responsiveness (at least with regard to the inductions considered in the present study), with several exceptions.