From the 1930s Davis-Husband scale to the modern Elkins Hypnotizability Scale — here’s how we measure trance depth and why it matters clinically.
Why Measuring Hypnotic Depth Matters
In clinical practice, knowing whether a client is in a light, medium, or deep trance helps the practitioner choose appropriate interventions. Deeper states are generally associated with greater responsiveness to therapeutic suggestions, while lighter states may be better for conversational approaches and ego-strengthening work [1]. Without a reliable measurement framework, practitioners rely on subjective observation — eye catalepsy, breathing rate, facial muscle relaxation — which varies enormously between clients. Standardised scales provide a common language for research and training [2].
The Davis-Husband Scale (1931)
The first systematic attempt to measure hypnotic depth was published by Lawrence Davis and Richard Husband in 1931 [1]. Their scale categorised depth along a continuum from “insusceptible” through “hypnoidal,” “trance,” “deep trance,” and “stuporous.” Each level was tied to specific observable behaviours: fluttering eyelids at the lightest end, partial amnesia in the mid-range, and post-hypnotic hallucinations at the deepest levels. While groundbreaking for its time, the scale relied entirely on external observation — it could not account for the client’s internal experience of trance [1].
Tart’s Self-Report Revolution (1970)
Charles Tart introduced a fundamentally different approach: ask the person in trance how deep they feel they are [2]. His self-report scale used a 0–100 numeric rating, where 0 was fully alert and 100 was the deepest trance imaginable. This tapped into the subjective experience of hypnotic depth — what Tart called “the single most important variable” in hypnosis research. His work showed that self-reported depth correlates moderately well with behavioural measures, but also reveals dimensions of trance that external observers miss [2].
The Elkins Hypnotizability Scale (2015)
The Elkins Hypnotizability Scale (EHS), developed by Gary Elkins and colleagues, represents the modern standard [3]. Designed specifically for clinical settings, it takes about 10–15 minutes to administer, includes a standardised induction, and measures response to a graded series of suggestions (motor, challenge, cognitive, and amnesia items). The clinical form (EHS-CF) is available for even briefer assessments. Test-retest reliability is strong, and the scale has been validated in French, Spanish, and other languages [3].
Choosing a Scale for Your Practice
Not every client needs formal depth measurement in every session, but having a structured tool is valuable. The Elkins scale is the best starting point: evidence-based, quick to administer, and trackable over time. Tart’s self-report scale can supplement this for clients who are good at introspecting. The Davis-Husband scale remains useful for quick behavioural checks but should not be used as a standalone measure [1, 3]. Most importantly, use the same method consistently so you can track how each client’s responsiveness changes over time.
References
- Davis, L. W., & Husband, R. W. (1931). A study of hypnotic susceptibility in relation to personality traits. The Journal of Abnormal and Social Psychology, 26(2), 175–182. DOI: 10.1037/h0074985
- Tart, C. T. (1970). Self-report scales of hypnotic depth. International Journal of Clinical and Experimental Hypnosis, 18(2), 105–125. DOI: 10.1080/00207147008415909
- Kekecs, Z., Roberts, L., & Na, H. (2021). Test-Retest Reliability of the Stanford Hypnotic Susceptibility Scale, Form C and the Elkins Hypnotizability Scale. International Journal of Clinical and Experimental Hypnosis, 69(1), 142–161. DOI: 10.1080/00207144.2021.1834858