EEG Theta/Beta Ratio Calculations Differ Between Various EEG Neurofeedback and Assessment Software Packages: Clinical Interpretation

Abstract

The quantitative electroencephalographic (QEEG) theta/beta power ratio (TBR) has been shown to have an association with attention-deficit hyperactivity disorder (ADHD), with a previous tacit assumption of equivalence across hardware and software systems. Therefore, the International Collaborative ADHD Neurofeedback (ICAN) randomized clinical trial used a fixed TBR ≥ 4.5 cutoff as measured by the Thought Technology Monastra-Lubar Assessment Suite as an inclusion criterion, 1.5 SD above norms collected with that system. However, a difference was noted between the TBR calculated by that assessment suite and the TBR computed by EEGer, the neurofeedback software used for treatment, leading us to investigate the discrepancy. The difference may arise from different calculation methods. This article explains and compares various computational methods used to calculate and display EEG values, including TBR, elucidating why the values are not equivalent across equipment and software programs. Two major sources of variance are (1) how “spectral leakage” at the ends of bands is handled and (2) whether voltages of bins within a band are first averaged and then squared to get bandwidth power or are first squared to get power (turning negative voltages into positive power) and then averaged to get the bandwidth power; the latter method results in higher band power. This article compares methods of computing the TBR. Biofeedback practitioners and investigators should be aware of the algorithms their systems use when interpreting TBRs and require normative comparison data collected with the same system.