A person who is hypnotized displays certain exceptional characteristics and propensities, compared with a non-hypnotized subject, most notably hyper-suggestibility, which some authorities have treated url a sine qua non of hypnosis. For example, Clark L. Hull, probably the first exceeding empirical researcher in the field, wrote,
The authors thought-out a total of 444 studies on hypnotherapy published prior to 2002. By selecting the best quality and most suitable research designs for meta-analysis they narrowed their focus down to 57 controlled trials. These showed that on boilerplate hypnotherapy achieved at least 64% success compared to 37% improvement among untreated force groups. (Based on the figures produced by binomial effect size display or BESD.)