Herbert Spiegel developed the Hypnotic Induction Profile when he was at Columbia University. Due to its low success rate of 75%, the field of psychiatry in reports has found this not high enough for predictive purposes.
Spiegel devised a simple 5 stage scale based on getting the person to imagine they have something to look up for, where zero is where the eyes stare straight forwards.
However, this more likely shows willingness to be hypnotised rather than being more suggestible. Someone with a scale of 0 is basically not interested.
Herbert Spiegel was involved in the ‘Sybil’ case in the 1960s where Shirley Ardell Mason was diagnosed with Multiple Personality Disorder, sparking a new set of medical analysis into that disorder. This was later redefined as Dissociative Identity Disorder. Spiegel discovered that she was highly hypnotisable. He found that her therapist was identifying experiences in her life as unique personalities and saw that these ‘personalities’ were merely a game play by Mason.