Statistical analysis
anxiety, MEQ-30
Linear mixed-effects models (LMMs) were constructed to test the relationship between doses, timepoints, and the response variables of intensity, anxiety, HR, DMT plasma concentrations, ASC scores and MEQ-30 scores. LMMs exhibit several advantages over repeated measures Analyses of Variance (ANOVAs) in dealing with the present data: (1) LMMs control for the potential influence of random variables (i.e., subject-driven interindividual variability) by including them as random effects; (2) LMMs can cope with missing data; and (3) they are able to include grouping hierarchies such as the present partially crossed groups (i.e., each subject received multiple but not all DMT doses).LMM analyses were run in R (version 4.2.2) using the For variables that were measured at multiple timepoints (subjective intensity, anxiety, HR, and plasma DMT concentration), dose and timepoint were added as fixed effects, and the dependent variable was assessed via change scores from the placebo condition for the same subject at that given timepoint. For those models, both dose and time were treated as categorical variables, and the earliest timepoint (minute -8) of Dose 1 was specified as a reference. While the investigation of the differences between each pair of doses is of interest, the small sample size motivated us to reduce the number of comparisons by focusing the statistical analyses on contrasting higher doses against Dose 1. Consequently, we report the summary statistics of Dose 1 compared to placebo, and the added effects of higher doses compared to Dose 1. The resulting model for these outcome variables was specified as follows:
For variables that do not include a temporal dimension (5D-ASC and MEQ-30 scales), one LMM was fitted for each subscale. For these models, only Dose was added as a fixed effect, and analyses were performed on raw scores. The resulting model for these outcome variables was specified as follows:
For all mixed models, significance was estimated via the No statistical analysis was performed on the dimensions of the experience over time, as these were assessed retrospectively and hence were susceptible to recall bias. They are reported qualitatively to inform future studies employing acute experience sampling to investigate the extended DMT experience.