Table 2.

Characteristics of the included studies.

Study	Prevalence	Measurement	Exclusion	Ethnicity	IP associations
Wing et al. (19)	0.18a	GOPQ, lifetime	No criteria	Chinese	None reported
Spanos et al. (20)	0.08a	Custom-made, lifetime	No criteria	Unknown	None reported
Fukuda et al. (21)	0.15	Custom-made, lifetime	No criteria	Caucasian	None reported
Fukuda et al. (21)	0.09	Custom-made, lifetime	No criteria	Asian	None reported
Cheyne et al. (22)	0.12	WUSES, lifetime	No criteria	Unknown	Associations with other hallucinatory experiences
Wing et al. (23)	0.09a	GOPQ, lifetime	No criteria	Chinese	None reported
Buzzi and Cirignotta (24)	0.13a	Custom-made, lifetime	Medical condition	Caucasian	None reported
Cheyne and Girard (25)	0.14	WUSES, lifetime	No criteria	Unknown	Associations with intruder- and vestibular-motor experiences and fear
Abrams et al. (26)	0.40e	WUSES, lifetime	No criteria	Mix, 82% Caucasian	Associations with childhood sexual abuse
Ramsawh et al. (27)	0.27e	Custom-made, lifetime	No criteria	Mix, 83% Caucasian	None reported
Solomonova et al. (28)	0.65b	WUSES, lifetime	Seeb below	Unknown	Associations with distress
Jiménez-Genchi et al. (29)	0.11a	Custom-made, lifetime	No criteria	Mexican	None reported
Paradis et al. (30)	0.04	USEQ, lifetime	No criteria	Mix, 71% Caucasian	None reported
Young et al. (31)	0.31d	GOPQ, lifetime	Seec below	Miao	None reported

GOPQ, Ghost Oppression Phenomenon Questionnaire with interview component; USEQ, Unusual Sleep Experiences Questionnaire; WUSES, Waterloo Unusual Sensory Experiences Survey.

^aThese estimates include episodes of sleep paralysis with pressure on the chest with or without experiencing difficulties with breathing.

^bThis sample selectively recruited participants in online groups concerned with sleep paralysis and related issues; it selected on a correlate of outcome. Hence the prevalence estimate derived in this study is not representative for the general population.

^cThis sample is not representative for the general population. It sampled among Hmong immigrants in order to learn about the astonishingly high mortality rate due to the “sudden unexplained death syndrome,” a sleep-related disorder.

^dIn this sample, participants were asked whether they experienced “dab tsog,” which in the Hmong culture refers to “a visit from the chest-pressing spirit,” which is equivalent to the Incubus phenomenon and a specific cultural stress regarding issues like this.

^eRecruited through newspaper advertisements, thus, self-selection bias is likely.