You will softly and silently vanish away And never be met with again --Lewis Carroll, The Hunting of the Snark
If something exists, you can measure it, at least potentially, I was taught in my experimental psychology courses. And if you cannot measure it in some way, then it doesn't exist. So. By the middle of the Twentieth Century, a number of hypnotic suggestibility, susceptibility, and depth scales had been developed, culminating with the Harvard Group Scale of Hypnotic Susceptibility, which even today remains the gold standard of such measurements. But what does it really teach us about hypnosis and how to use it?
The Harvard Group Scale of Hypnotic Susceptibility, Form A (Shor & Orne, 1962) is modeled after the experimental approach originally begun by Clark Hull (1933). It contains a script consisting of a light hypnotic induction, followed by a list of twelve suggestions in increasing order of difficulty, from "easy" ones which almost anyone can pass, to more difficult items such as the inability to shake one's head "no" when challenged, or amnesia for most of the test items until after a prearranged signal has been given. Since its initial publication in 1962, the test has been used in studies all over the world, in order to give us a greater understanding of individual differences in suggestibility.
In a typical administration, in a class setting of about thirty people, there are from one to three high responders who obtain a perfect score of twelve on the test, one or two people at the low end who are just sitting there with their eyes open, looking around the room with a mixture of curiosity and boredom, and the rest manifesting varying degrees of responsiveness in between. Data of this type have yielded a great deal of useful information about differences between high and low responders over the years, and I have collected some of it myself. For example, I found that highly hypnotizable people convincingly reported having undergone a Fundamentalist experience of "Salvation," while low scorers did not (Gibbons & DeJarnette, 1972).
Now let's perform a thought experiment, imagine if you will, that the Harvard Group Scale is being given to a class of introductory psychology students, when a person dressed in a police uniform bursts into the room and says in a loud, commanding voice, "There is an active shooter in the building. Everybody get under your desk and await further instructions!!"
Even if such an announcement is a hoax (i.e., a cleverly-designed suggestion) thought up by a disgruntled student to disrupt the orderly running of campus activities, if it were to be conducted in a sufficiently convincing manner, everyone in the class -- including the instructor -- would probably cower under their desks in a high state of emotion. What happened to the individual differences in suggestibility which the Harvard Group Scale was supposed to measure? They simply vanished, as everyone scrambled for shelter.
A high degree of responsiveness to the impostor's suggestions would occur regardless of how an individual student might have scored on the suggestibility test which was currently underway. Notice also that the subjects would probably have been totally involved in the content of the impostor's suggestions: trembling, feeling frightened, weeping, crying out in alarm, and so on.
Even though many useful applications have been found using the Harvard Group Scale, suggestibility only appears to be a trait of personality, because our experiments are designed and carried out in a standardized group setting such as a classroom. But if a suggestion is believable enough, or if you modify the setting in which it is measured, as in the hypothetical example just mentioned, individual differences in responsiveness can change dramatically, or even disappear.
Many practicing hypnotists will assure you that in clinical settings, these measured differences are less than reliable, because the measurements were collected in a narrow setting which did not sufficiently represent the real world.. Once their doubts and fears have been eliminated by an appropriate pre-hypnotic talk, some people respond to hypnosis poorly, most people respond to some extent, and a few others respond extremely well. A number of techniques have been developed to "hypnotize the un-hypnotizable" by convincing the low-responders that they too have been hypnotized. When this is done, they not only respond better on suggestibility tests then those who have not accepted this idea, but they also respond better in therapy (Lynn & Kirsch, 2006).
The “Snark” of the hypnotic trance was merely a “Boojum” of the active imagination. Regardless of whether or not you experience a trance during a hypnotic procedure, you're hypnotized if you think you are!
I do not hesitate to share this idea with my hypnotically gifted clients, because it provides an oft-needed boost to their self-esteem to realize that they are on the cutting edge of evolution, and it also enhances the professional image of hypnosis itself
As I was discussing this idea with one of my more hypnotically-gifted clients the other day, he added, "And the next breakthrough is going to be spiritual." Roy Hunter is currently working on a second book on hypnosis and spirituality, and many others are preparing workshops on blending the two.
With regard to the question of what makes a hypnotic intervention effective, I like to quote Steve Lynn's excellent summary of our Induction chapter in the American Psychological Association's Handbook of Clinical Hypnosis:
. . .how clients respond to suggestions depends less on the nature and success of a particular induction than on the following variables: (a) clients' prehypnotic attitudes, beliefs, intentions, and expectations about hypnosis; (b) their ability to think, fantasize, and absorb themselves in suggestions; (c) their ability to form a trusting relationship with the hypnotist; (d) their ability to interpret suggestions appropriately and view their responses as successful; (e) their ability to discern task demands and cues; (f) their ongoing interaction with the hypnotist; and (g) the appropriateness of the therapeutic methods and suggestions to treating the presenting problem. . . . Accordingly, clinicians should devise inductions and suggestions with these variables in mind and tailor their approach to the unique personal characteristics and agenda of each client they encounter," (Gibbons & Lynn, 2010, p. 289).