Measuring hypnotizability: the case for self-report depth scales and normative data for the long Stanford scale.

Conventional suggestion-based tests of hypnotizability have been criticized because they confound hypnotic and nonhypnotic suggestibility. One way around this might be to measure hypnotizability in terms of differences in suggestibility before and after hypnotic induction. However, analysis of data from a 1966 classic study by Hilgard and Tart confirms that difference scores are subject to statistical and methodological problems. Simple verbal hypnotic depth scales are presented as a useful alternative. They correlate well with conventional suggestion-based measures and enable the presence of hypnosis to be indexed independently of formal hypnotic induction procedures. Criticisms of depth scales are addressed, and normative data for the Long Stanford Scale of hypnotic depth are presented, along with data lending empirical support for the construct validity of depth reports.