Computational protocol: Social Cognition and Interaction in Chronic Users of 3,4-Methylenedioxymethamphetamine (MDMA, “Ecstasy”)

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Protocol publication

[…] We performed the statistical analyses with SPSS 23.0 for Windows. Quantitative data were either analyzed by means of Student’s t tests (only demographic data), Mann-Whitney tests, or 2-way ANCOVA. Frequency data were analyzed by means of Pearson’s chi-square tests. We used an alpha level of .05 for all statistical tests. In the ANCOVAs applied to compare empathy between MDMA users and controls, we introduced group and sex as fixed factors, and verbal IQ as a covariate, because it was consistently shown that men are less empathic that women (; ; ; ) and because verbal IQ has been proposed to be linked to empathy measures before (). Analyzing social decision-making with ANCOVAs, sex was used as a second covariate to verbal IQ given that age is correlated with prosocial behavior (). We investigated the association between clinical measures and empathy and the association between plasma OXT values and empathy within MDMA users with correlation analyses (Pearson’s product-moment and Spearman’s rank correlation, respectively) whereby we applied a significance threshold of P<.01 to avoid alpha error accumulation. To be able to assess the strength of group differences and their practical significance between controls and MDMA users, Cohen’s d effect sizes were calculated based on the means and pooled SDs of the 2 groups ().To analyze potential cofactors of cognitive empathy, we regressed the CES on the demographic variables age, sex, years of education, and verbal IQ (forced entry) over all participants and over MDMA users only. To analyze drug effects (within MDMA users) on cognitive empathy, we regressed CES on the MDMA hair analyses while retaining those demographic variables in the model that were significantly associated with CES. Because our MDMA user group showed, although minimal, co-consumption of other drugs, we additionally added amphetamine and cocaine hair analyses together with self-reported measures of cannabis, alcohol, and nicotine consumption into the model according to previously published investigations of MDMA users (). Because some of the drug use variables displayed a right-skewed distribution, we log-transformed (log10) these data after adding the constant 1 to those variables that included 0 values.Based on a posthoc power analysis (after participant’s drug use was confirmed by hair analyses) with G*Power 3.1.9.2 (), the main effects of the ANCOVAs in this study have an alpha-error probability of 5% and a power of 80% (assumed 6% variance explained by special effect, 24% variance explained by the covariates, and 70% error variance). The power analysis for our regression model investigating MDMA’s effect on cognitive empathy within MDMA users revealed a power of 80% (one-tailed, assumed 13% variance explained by predictor, 12% by verbal IQ and 75% residual variance) (; ). […]

Pipeline specifications

Software tools SPSS, G*Power
Application Miscellaneous
Organisms Homo sapiens
Diseases Glaucoma, Open-Angle
Chemicals Oxytocin, N-Methyl-3,4-methylenedioxyamphetamine