Abstract

The Harvard Group Scale of Hypnotic Susceptibility (HGSHS:A) has proven to be a reliable and efficient measure of hypnotizability (Siuta, 2010). However, the psychometric properties of the posthypnotic amnesia suggestion on this scale lack integrity (Sadler & Woody, 2004; Piesbergen & Peter, 2006). It is hypothesized that the ambiguously written instructions explaining the recall test to participants are obscuring measurement, resulting in non-amnesic participants being scored amnesic. To show participants can be scored amnesic for reasons not attributable to the suggestion, 81 participants were administered the HGSHS:A without the amnesia suggestion. No difference in amnesia pass rate was observed between this group compared to 78 participants administered the standard HGSHS:A. Modifying the instructions to more directly explain the task to participants significantly lowered the frequency of passing this suggestion. In addition, no lows were scored amnesic and the concordance between behavioural and subjective scores was improved with the new instructions. Retesting the modified instructions on participants not administered the amnesia suggestion (N = 65) resulted in participants nevertheless being scored amnesic. The results from this study indicate that 1) the HGSHS:A scoring is improperly classifying participants as amnesic 2) the modified instructions better capture the classic suggestion effect 3) a significant proportion of participants experience difficulty remembering the hypnotic suggestions post-session, regardless of whether a suggestion for amnesia is administered. It is recommended that the written amnesia test instructions on the HGSHS:A be modified.