Three times NO: no relationship between frontal alpha asymmetry and depressive disorders in a multiverse analysis of three studies.
Frontal alpha asymmetry (FAA) is one of the most common electrophysiological measures in research on depressive disorders (DD). Many previous studies reported a relatively higher alpha band power in the left versus right frontal channels (left-sided FAA) in people with DD compared to healthy controls. Recently, however, multiple studies failed to replicate this finding and a meta-analysis has cast doubt on the relationship between FFA and DD (van der Vinne et al., 2017). To test the robustness and reproducibility of the relationship between FAA and DD we conducted a multiverse analysis of resting state EEG data from three independent studies with 218 participants in total. We performed 81 analyses altogether - some replicatory and other improving on the methodology used in past FAA studies -differing in: a) channel vs source level signal: using average reference, current source density or DICS beamforming; b) channel pairs selection and correction for multiple comparisons; c) statistical approach: group contrasts vs linear regression. Only two of the 81 analyses revealed significant results - an outcome expected with a 5% type I error rate (p = 0.917, binomial test). Therefore, the conducted analyses do not provide a basis to reject the null hypothesis of no relationship between resting state FAA and DD in spite of (or maybe due to) various methodological improvements. We conclude the paper by discussing theoretical assumptions underlying the FAA and suggest a list of guidelines for improving and expanding the EEG data analysis in future FAA studies. Significance StatementFor decades, the frontal alpha asymmetry (FAA) - a disproportion in EEG alpha oscillations power between right and left frontal channels - has been one of the most popular measures of depressive disorders (DD) in electrophysiology studies. Patients with DD often manifest a left-sided FAA: relatively higher alpha power in the left versus right frontal lobe. Recently, however, multiple studies failed to confirm this effect, questioning its reproducibility. Our purpose is to thoroughly test the validity of FAA in depression by conducting a multiverse analysis - running many related analyses and testing the sensitivity of the effect to changes in the analytical approach - on data from three independent studies. Overall, our results do not support the claim about the FAA-DD relationship.