A Rasch analysis of the Stanford Hypnotic Susceptibility Scale, Form C

The psychometric structure of the Stanford Hypnotic Susceptibility Scale, Form C (SHSS:C) was tested in a Rasch analysis using data from 279 subjects. The Rasch model is the model of choice because it justifies the use of the sum of the item scores as a measure for the underlying construct. Rasch analysis revealed that use of a single sum score (number of suggestions passed) to express hypnotic ability is not sufficiently justified. However, the omission of the mosquito-hallucination and anosmia items (Items 3 and 9) rendered this short 10-item form of the SHSS:C sufficiently compatible with requirements of one-dimensionality, local stochastic independence, and equi-discriminability. Hence, the 10-item form justifies use of a sum score.