Materials & Methods:
Study design
Our objective was to investigate whether people with a history of migraine aura are more likely to have NDE, and vice versa, than people without migraine aura. We used an online platform, Prolific Academic (
https://prolific.ac/), to recruit an international sample of laypeople. Like Amazon’s Mechanical Turk, Prolific Academic is a crowdsourcing online platform to recruit human subjects that can be used for research purposes (Kondziella, Dreier &; Olsen, 2019; Kondziella, Cheung &; Dutta, 2019) and that compares favorably in terms of data quality, including honesty and diversity of participants (Peer et al., 2017). Participants were recruited without any filters except for English language and age ≥18 years, and we excluded participants who had been enrolled in our previous study on NDE and REM intrusion (Kondziella, Dreier &; Olsen, 2019). The study was announced under the headline “Survey on near-death experiences and headache” using the following text: “We wish to explore the frequency with which near-death experiences occur in the public. This should take no more than 1.5 minutes on average (a little bit longer, if you have had such an experience, and a little bit less, if you haven’t). You will be paid 0.20$ after completing the survey. Please note that we might use your anonymous answers when writing a paper.”
From all participants, we collected information about age, gender, place of residence and employment status (data provided automatically by Prolific Academic); if they had frequent headaches; if yes, if these headaches could last longer than 4 hours and were associated with visual or non-visual aura (Kaiser et al., 2019); if participants ever had an NDE; if yes, if this experience occurred in a truly life-threatening situation or in a situation that just felt so; if the experience was neutral, pleasant or unpleasant; and all participants with an NDE were asked to provide information about all 16 items of the GNDES, the most widely used standardized tool to identify, confirm and characterize NDE in research (Greyson, 1983). Like in our previous study (Kondziella, Dreier &; Olsen, 2019), NDE was defined by a GNDES score ≥7. Participants with an NDE (and those who claimed an NDE but scored 6 or less points on the GNDES) were also given the opportunity to describe this in their own words (optional).
Statistics
Using a very high population size (300,000,000), a confidence level of 95% and a margin of error of 5%, we estimated the required sample size to be 384 participants. However, since previous studies have estimated the frequency with which NDE occur in the public to be 5-10%, including our own on NDE and REM intrusion (Kondziella, Dreier & Olsen, 2019), we decided to enroll approximately 1000 participants to identify an estimated number of 100 individuals with an NDE. In univariate analysis, associations between potential predictors (age, gender, migraine aura) for NDE were examined using chi-square test and t-test for independent samples. Additionally, we used multiple logistic regression to analyze the association between migraine aura and NDE adjusted for age and gender. The level of significance was 0.05 (two-sided) for all statistical tests. Statistical analysis was performed with SPSS 23.0 (IBM, Armonk, NY, USA).
Ethics
Participants gave consent for publication of their anonymous data. Participation was voluntary, anonymous and restricted to those aged 18 years or older. Participants received a monetary reimbursement after completing the survey, in accordance with the Prolific Academic’s ethical rewards principle (≥ $6.50/h). The Ethics Committee of the Capital Region of Denmark waives approval for online surveys (Section 14 (1) of the Committee Act. 2;
http://www.nvk.dk/english).
Data Availability Statement
The de-identified raw data are provided in the online supplemental files.