Indirect Suggestion

The first investigation of indirect suggestion was in 1983. Indirect Versus Direct Hypnotic Suggestions — An Initial Investigation: A Brief Communication did a systematic comparison and found that there were no significant behavioral differences between direct and indirect methods of suggestion. The participants did feel more deeply hypnotized using indirect methods, and high hypnotizables males felt more "in charge" and aware during indirect suggestions.

In 1987, Inductions versus suggestions: Effects of direct and indirect wording on hypnotic responding and experience did a study with 235 participants and a rigorous methodology. They found that direct suggestions produced greater subjective involuntariness than indirect suggestions, but that there were no significant differences in objective responding between methods. The paper suggested that permissiveness in indirect suggestions may actually accentuate feelings of control.

In 1988, Direct Versus Indirect Suggestions: A Conceptual and Methodological Review reviewed 29 studies covering direct vs indirect suggestions. Based on the studies, they found that suggestion style has minimal effect on objective responding, insufficient evidence that low-susceptible subjects respond better to indirect methods, and suggested that terms like "direct" and "indirect" might be more "buzz words" than meaningful scientific distinctions. This pretty much wrapped it up as far as the research went.

In 1993, The Effects of Direct Versus Indirect Hypnotic Suggestion on Pain in a Cold Pressor Task found no significant difference between direct and indirect techniques for pain reduction. They did find that high-susceptible subjects showed greater pain reduction overall, but indirect methods were not more effective for low-susceptible subjects as they hypothesized.

And finally, in 2003 On the efficacy of hypnosis: a meta‐analytic study looked at 57 randomized clinical studies and found that only 16 studies used indirect suggestions. The clinical reality is that most therapeutic applications still rely on direct methods despite theoretical interest in indirect approaches.