One explanatory basis for the discrepancy of reported prevalences of sleep paralysis among healthy respondents.

In a previous study, the author and coworkers found 39.8% of healthy young adults had experienced sleep paralysis. Some other studies reported prevalence as about the same or higher (i.e., 40.7% to 62.0%) than that previous estimate, while yet other studies, including Goode's work cited by ASDC and ASDA classifications, suggested much lower prevalences (i.e., 4.7% to 26.2%). The author tested the hypothesis that this discrepancy among the reported prevalences is partly due to the expression used in each questionnaire. University students who answered the questionnaire using the term 'transient paralysis' reported the lower prevalence (26.4%), while the second group of respondents who answered the questionnaire using the term kanashibari, the Japanese folklore expression for sleep paralysis, gave the higher prevalence (39.3%). The third group who answered the questionnaire with the term 'condition,' probably a rather neutral expression, marked the middle (31.0%) of these.