Factor analysis of the mystical experience questionnaire: A study of experiences occasioned by the hallucinogen psilocybin
Exploratory factor analysis of responses from 1,602 psilocybin users retained 30 items from the Mystical Experience Questionnaire and revealed a reliable four‑factor structure (unity/noetic/sacredness; positive mood; transcendence of time/space; ineffability), with convergent and construct validity and replication in an independent sample (N=440). These results provide initial evidence that the 30‑item MEQ is a valid, reliable tool for measuring single hallucinogen‑occasioned mystical experiences.
Authors
- Griffiths, R. R.
- Johnson, M. W.
- Leoutsakos, J. S.
Published
Abstract
A large body of historical evidence describes the use of hallucinogenic compounds, such as psilocybin mushrooms, for religious purposes. But few scientific studies have attempted to measure or characterize hallucinogen‐occasioned spiritual experiences. The present study examined the factor structure of the Mystical Experience Questionnaire (MEQ), a self‐report measure that has been used to assess the effects of hallucinogens in laboratory studies. Participants (N = 1,602) completed the 43‐item MEQ in reference to a mystical or profound experience they had had after ingesting psilocybin. Exploratory factor analysis of the MEQ retained 30 items and revealed a four‐factor structure covering the dimensions of classic mystical experience: unity, noetic quality, sacredness (F1); positive mood (F2); transcendence of time/space (F3); and ineffability (F4). MEQ factor scores showed good internal reliability and correlated with the Hood Mysticism Scale, indicating convergent validity. Participants who endorsed having had a mystical experience on psilocybin, compared to those who did not, had significantly higher factor scores, indicating construct validity. The four‐factor structure was confirmed in a second sample (N = 440) and demonstrated superior fit compared to alternative models. The results provide initial evidence of the validity, reliability, and factor structure of a 30‐item scale for measuring single, hallucinogen‐occasioned mystical experiences, which may be a useful tool in the scientific study of mysticism.
Research Summary of 'Factor analysis of the mystical experience questionnaire: A study of experiences occasioned by the hallucinogen psilocybin'
Introduction
Mystical experiences are reported across religious traditions and historical accounts, with prior questionnaire research identifying core features such as unity, sacredness, ineffability, peace and joy, transcendence of time and space, and a noetic sense of objective truth. Although lifetime measures of mysticism (for example, Hood's Mysticism Scale) have been studied psychometrically, relatively little empirical work has focused on single, discrete mystical events or on mystical experiences occasioned specifically by hallucinogens such as psilocybin. Recent laboratory studies indicate that psilocybin can reliably occasion mystical-type experiences that in some cases predict lasting increases in well-being, yet the principal self-report instrument used in that literature, the Mystical Experience Questionnaire (MEQ), had not been formally validated or factor-analysed for single event assessment. Maclean and colleagues set out to evaluate the psychometric properties and factor structure of the MEQ. Using a large web-based convenience sample of individuals who reported having had a profound experience after ingesting psilocybin mushrooms, the study aimed to (1) explore the latent factor structure of the 43-item MEQ via exploratory factor analysis (Study 1), (2) assess reliability and convergent and construct validity against the 32-item Mysticism Scale, and (3) test the resulting factor model in an independent sample using confirmatory factor analysis (Study 2). The goal was to produce a validated, reliable scale for quantifying single, hallucinogen-occasioned mystical experiences.
Methods
Participants were recruited primarily through web-link advertisements, e-mail invitations, and online communities interested in spirituality and psychoactive substances. Study 1 data collection occurred during two recruitment rounds (May–June 2010 and July 2010). Inclusion criteria required participants to be 18 years or older, fluent in English, to have taken an active dose of psilocybin mushrooms producing moderate to strong effects, and to report a profound, personally meaningful psilocybin session. Of 1,720 respondents, 1,602 (93%) met all inclusion criteria and completed the survey. Study 2 used an available convenience sample collected in a similar manner (N = 440 complete MEQ responses). The online survey (administered via SurveyMonkey) collected demographics, lifetime hallucinogen use, and details about a single chosen psilocybin session. For Study 1 the 43 MEQ items were intermixed with 57 distracter items; in Study 2 only the 43 MEQ items were presented. Each MEQ item was rated on a six-point intensity scale (0–5). Participants also completed a modified, single-event version of the 32-item Mysticism Scale (items rated on a nine-point scale) to permit convergent validity analyses. Additional session-specific items included three questions from a Persisting Effects Questionnaire and an optional written description of the experience. Statistical analysis focused on the MEQ factor structure, reliability, and validity. Because item responses were sparse and non-normally distributed, polychoric correlations were used. In Study 1 the polychoric correlation matrix of 43 items underwent parallel analysis (1,000 draws) to guide factor extraction, followed by exploratory factor analysis (EFA) with promax rotation to allow correlated factors. Items were eliminated if they failed to load ≥ .40 on any factor, loaded ≥ .40 on more than one factor, or had high uniqueness (> .60). A single round of item elimination was predetermined; a second parallel analysis was run on the reduced item set to confirm factor number. Standardised factor scores were computed and group comparisons used t tests and ANOVA. Study 2 performed confirmatory factor analyses (CFA) in Mplus v.6.1 using categorical responses and a robust weighted least-squares estimator to compare three models: two established three-factor models derived from prior mysticism research (Hood and Stace variants) and the four-factor model emerging from Study 1. Fit indices reported included RMSEA, CFI and TLI, with RMSEA < .10 and CFI/TLI > .90 considered suggestive of acceptable fit given sample size considerations.
Results
Study 1 sample characteristics: N = 1,602, 50% female, wide age and country representation, generally well educated and reporting satisfactory life satisfaction. When asked to define their religiousness/spirituality, 70% identified as “spiritual but not religious,” 13.5% as “spiritual and religious,” 16% as “neither,” and <1% as “religious but not spiritual.” Exploratory factor analysis of the 43 MEQ items indicated that a four-factor solution was most appropriate (parallel analysis and scree inspection). Thirteen items were removed for low primary loadings, cross-loadings, or high uniqueness, leaving 30 items in the final model. The promax-rotated four-factor solution explained on average 57% of the variance across items (communalities range = 39–78%). Factor 1 comprised items related to internal and external unity, noetic quality and sacredness; Factor 2 reflected positive mood; Factor 3 represented transcendence of time and space; and Factor 4 captured ineffability. Reliability estimates were high for the 30-item revised MEQ (Cronbach's alpha = .933) and acceptable to good for the four subscales (Factor 1 = .926; Factor 2 = .831; Factor 3 = .810; Factor 4 = .800). Convergent validity with the Mysticism Scale was strong: total Mysticism Scale correlated r = .81 (p < .001) with total MEQ, and MEQ Factor 1 correlated r = .79 (p < .001) with the Mysticism Scale. Correlations were more modest for the other MEQ factors (Factor 2 r = .55; Factor 3 r = .47; Factor 4 r = .41; all p < .001). For construct validity, 1,410 participants (88%) endorsed having had a mystical experience during a psilocybin session; these participants had significantly higher MEQ factor scores and higher Mysticism Scale scores than those who did not endorse a mystical experience (p < .001). Study 2 (N = 440) characterised a different demographic profile (predominantly male 88%, mean age ≈ 28 years, lower formal education levels); 88% again endorsed a spiritual experience after psilocybin. CFA compared the Hood and Stace three-factor models with the four-factor “Psilocybin” model. The Hood and Stace models failed to meet fit cutoffs (Hood: RMSEA = .110, CFI = .88, TLI = .88; Stace: RMSEA = .109, CFI = .89, TLI = .88). The four-factor Psilocybin model showed acceptable fit (RMSEA = .074, CFI = .95, TLI = .94). Factor loadings in the Psilocybin model were high (> .65) and factors were intercorrelated; on average the model explained 64% of the variance per item (residual variances range = 16–54%). Reliability estimates in Study 2 were consistent with Study 1 (30-item alpha = .957; Factor alphas = .946, .831, .887, .864).
Discussion
Across two web-based samples, the investigators found that a 30-item revision of the MEQ is psychometrically robust for measuring single, psilocybin-occasioned mystical experiences. The EFA in Study 1 identified four correlated factors — a primary “mystical” factor combining unity, noetic quality and sacredness, plus separate factors for positive mood, transcendence of time and space, and ineffability — and the four-factor solution was confirmed in an independent convenience sample by CFA. Both total and subscale MEQ scores demonstrated excellent internal consistency and convergent validity with the established Mysticism Scale, and participants who self-reported having had a mystical experience after psilocybin scored higher on the MEQ, supporting construct validity. The authors note that the principal novel finding is the combination of internal and external unity with noetic quality and sacredness on a single factor, a pattern that departs from some earlier lifetime-focused analyses that distinguished introvertive and extrovertive unity. They propose several possible explanations: the MEQ's particular item wording and structure, measurement of a single time-limited event rather than lifetime experience, and the characteristics of the self-selected sample (predominantly “spiritual but not religious”). The discussion situates findings relative to previous factor-analytic work, noting both consistencies with more recent studies that also found unity and noetic quality to co-load, and contrasts with older models that separated phenomenology from interpretative elements. Key limitations acknowledged by the study team include the self-selected, convenience sampling that may bias results toward positive spiritual experiences, and the need for further confirmatory work to test reliability (including test–retest) and validity in other populations and contexts. The authors caution that while the revised MEQ appears suitable for laboratory studies of classic hallucinogens and informal naturalistic settings, its appropriateness for other populations or modalities is not established. They recommend additional confirmatory factor-analytic studies across diverse samples and complementary laboratory and survey research to further characterise hallucinogen-occasioned mystical phenomena.
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RESULTS
Three CFA models were fit to the data set: (1) the "Hood" three-factor model (Introvertive factor; Extrovertive factor; and Interpretation factor); (2) the "Stace" three-factor model (identical to the Hood model except ineffability itemswere moved to the Interpretation factor); and (3) the "Psilocybin" four-factor model. Models were fit in MPLUS v. 6.1, using categorical responses and a robust, weighted least-squares estimator. Fit indices included the RMSEA (residual mean square error of approximation), CFI (conditional fit index), and TLI (Tucker-Lewis index). We considered RMSEA values < .10 (Browne and Cudeck 1992) and CFI/TLI values > .90to be suggestive of adequate fit. Given the large sample size, the chi-square goodness-of-fit test was not appropriate. Both the Hood (RMSEA = .110; CFI = .88; TLI = .88) and Stace models (RMSEA = .109; CFI = .89; TLI = .88) failed to meet the cutoff values indicating acceptable model fit. In contrast, the four-factor Psilocybin model demonstrated better fit than the Hood and Stace models and exceeded the cutoffs for acceptable fit (RMSEA = .074; CFI = .95; TLI = .94). Factor loadings for the Psilocybin model were high (> .65; Table) and the factors were intercorrelated (Table). On average, the four-factor structure explained 64 percent of the variance in each item (range of residual variance values = 16-54 percent). As in Study 1, alpha reliability estimates indicated excellent internal consistency for the 30-item scale (alpha = .957) and good internal consistency for all four subscales (Factor 1 = .946; Factor 2 = .831; Factor 3 = .887; Factor 4 = .864).
CONCLUSION
In two web-based survey studies, we examined the factor structure of a self-report measure, the MEQ, designed to measure single mystical experiences that resulted from ingesting the hallucinogen psilocybin. In Study 1, EFA of the 43-item MEQ revealed a four-factor structure. The 30 items retained in the final model represent a revised scale for measuring mystical experience, which shows approximately 90 percent overlap (in item wording) with the original scale proposed by. Both the revised MEQ (total scale) and the four provisional subscales demonstrated substantial convergent validity with the widely used Mysticism Scale. In support of the construct validity of the revised MEQ, participants who endorsed having had a mystical experience after ingesting psilocybin (in response to a single mystical experience probe question) had higher factor scores than participants who did not endorse having had a mystical experience. In a second convenience sample (Study 2), the four-factor structure was confirmed using confirmatory factor analysis, demonstrating that the revised MEQ is robust to differences in sample demographics (e.g., gender, education level) and inclusion/exclusion of distracter items. Results from both studies indicate excellent reliability (internal consistency) for the revised scale and good reliability for the factor-analyzed subscales. Thus, the revised MEQ appears to be a psychometrically sound instrument for assessing hallucinogen-occasioned mystical-type experiences. Although additional confirmatory factor analysis studies are necessary to verify the reliability (e.g., internal consistency, test-retest), validity (e.g., convergent, divergent), and factor structure of the MEQ in other participant samples and contexts, the factor scores may prove useful for quantifying other types of mystical experiences in future studies. It is important to consider whether the factor structure of the MEQ is consistent with previous literature on mystical experience. The primary loadings on the first factor of the MEQ represent what appear to be the most unique and salient features of mystical experience: unity, noetic quality, and sacredness; thus, we have labeled Factor 1 "mystical." The second factor comprises items related to "positive mood," including items that were previously considered by, but not by, to reflect sacred feelings (e.g., awe, amazement). The remaining factors comprise items related to "transcendence of time and space" (Factor 3), and "ineffability" (Factor 4). Thus, three of the four factors appear to each represent a specific feature of mystical experience as outlined by. However, the combination of internal unity, external unity, noetic quality, and sacredness on a single factor is novel. It is possible that this factor structure is unique to the particular characteristics of the MEQ, to the specific participant sample (individuals who have had a hallucinogen-occasioned mystical experience), and/or to the analysis of single (not lifetime) mystical experiences. Although we cannot draw a strong conclusion based on the present data, these possible interpretations can be explored in future research. Nonetheless, below we consider whether the MEQ factor structure is consistent with other factor analyses of lifetime mystical experience using the Mysticism Scale. The primary loadings on Factor 1 indicate that features of both internal and external unity are present during individual, time-limited psilocybin sessions and are represented by the same underlying factor. This pattern is in contrast to factor analysis studies of the lifetime Mysticism Scale that indicated a distinction between introvertive and extrovertive mysticism (see Hood 2003 for a review), as well as historical accounts that illustrated differences between internally and externally focused unity experiences. Importantly, although Stace distinguished between internal and external unity, he also emphasized that an individual could experience both types of unity, and that "[m]ystics in general do not distinguish between the introvertive One and the extrovertive One . . . it is an essential and explicit part of the message of many mystics that the external and internal unity are identical". Furthermore, other researchers have noted that a single individual can experience both forms of unity during a lifetime) and even during single, time-limited hallucinogen sessions. The present results are in line with a recent factor analysis study showing that internal and external unity items load on a single factor. Chen and colleagues) assessed lifetime mystical experiences in Buddhist monks and nuns using a combination of qualitative interview techniques and factor analysis of reported phenomena. During the interviews, the monks and nuns described a particular type of "unifying experience of self with everything," which the authors interpreted as a combination of internal unity and external unity. In order to quantify this experience for the purpose of factor analysis, the authors introduced a new facet of "internal unity") that was distinct from Hood's facet of "contentless unity (i.e., ego loss)"). In the subsequent factor analysis, a single factor represented the new facet of "internal unity" combined with Hood's facets of "external unity" and "inner subjectivity." These three facets are semantically consistent with nine of the 15 items in the first factor of the MEQ, suggesting that some of the features of psilocybin-occasioned unity experiences overlap with those described by Buddhist meditators. Along these lines, Chen and colleaguesproposed that the particular structure of mystical experience in their Buddhist contemplative sample might also describe experiences of some non-Buddhists, such as spiritually inclined individuals who are not religiously affiliated. The primary loadings on Factor 1 additionally indicate that noetic quality and sacredness are represented by the same factor as unity. This result contrasts with early factor analyses of the Mysticism Scale that supported a theoretical distinction between the phenomenological experience of unity and a person's interpretation of that experience (see Hood 2003 for a review). However, our results are at least partially consistent with more recent studies of lay Tibetan Buddhists) and Hindu, Muslim, and Christian individuals in India, which found noetic quality to load on the same factor as unity. Notably, early scholars such as Jamessuggested that noetic quality could reflect a feeling or perception during a mystical experience rather than a post hoc interpretation. Similarly, Stace suggested that sacred or divine feelings might be central to the unity experience. Participants in the present study endorsed sacred/holy feelings, a sense of reverence, and a sense of being at a "spiritual height" as relevant features of the unity experience occasioned by psilocybin. These sacred items are semantically consistent with some current definitions of sacredness as feelings of deep meaning (van der Lans 1996), respect, and reverence. Finally, it is important to acknowledge how participants' spiritual and religious beliefs may have influenced the factor analysis results. Whereas the majority of participants in previous studies of mystical experience were religiously committed (e.g., American Christians, Israeli Jews, Iranian Muslims, and Tibetan/Chinese Buddhists), participants in the present study overwhelmingly identified as "spiritual but not religious" (Study 1: 70 percent) or religiously unaffiliated (Study 2: 73 percent). Although it is not possible to disentangle the effects of psilocybin, spirituality, and religious affiliation in the present self-selected sample, the factor analysis results may still be germane to understanding the mystical experiences of "spiritual but not religious" individuals in the general population. National surveys indicate that 15-20 percent of Americans identify as "spiritual but not religious" (seefor a review) and empirical findings suggest that these individuals are more likely than the general population to have had mystical experiences). Thus, this demographic group may be a logical focus for future empirical studies of the causes, features, and consequences of mystical experience. We suggest that the scientific study of mysticism would be advanced by examining the structure of mystical experiences in groups of individuals who differ in self-identified spirituality, as a complement to the majority of published studies that have focused on religiously affiliated individuals. In conclusion, the factor analysis results provide initial evidence of the validity and reliability of a 30-item scale for measuring mystical experiences, the revised MEQ (see the Appendix). Because the present study was conducted in a large, heterogeneous sample of hallucinogen users, the results are likely generalizable to a range of naturalistic situations in which people choose to use hallucinogens. Although it is reasonable to assume that the results may be biased toward positive spiritual experiences (because participants self-selected into the study), the findings suggest that the MEQ is a psychometrically sound measure for laboratory studies of classic hallucinogens. However, the appropriateness of the scale for use in other populations or contexts is not directly supported by the present results. It will be necessary to explore the validity, reliability, and factor structure of the MEQ in additional confirmatory studies of different populations and modalities. Fortunately, web-based surveys are becoming popular tools in psychological research, including in research on hallucinogens, and several studies have demonstrated that questionnaires administered in this manner produce reliable, accurate, and psychometrically valid data. Both survey-and laboratory-based studies will continue to be important for characterizing the phenomenological effects of classic hallucinogens and for the empirical study of mystical experience.
Study Details
- Study Typeindividual
- Populationhumans
- Characteristicssurvey
- Journal
- Compound
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