“…In recent years, several nonlinear methods based on single-channel EEG signals such as fractal dimension ( Li et al, 2017 ; Nguyen, Wen, & Li, 2010 ), Bayesian analysis ( Nguyen-Ky, Wen, & Li, 2013 , Nguyen-Ky, Wen, & Li, 2014 ), phase-rectified signal averaging ( Liu, Chen, Fan, Abbod, & Shieh, 2016 ; Liu, Chen, Fan, Abbod, & Shieh, 2017 ) and entropy ( Li & Wen, 2016 ; Liang et al, 2015 ; Shalbaf, Saffar, Sleigh, & Shalbaf, 2017 ; Shalbaf, Saffar, & Sleigh, 2020 ) have been proposed for DOA assessment. Today, Bispectral index (BIS) monitoring is the most commonly used single-channel EEG to measure DOA during general anesthesia and has been widely accepted for its accuracy.…”