“…The principal outcomes differed among studies. For instance, one study focused only on the detection of pain [35], eight studies only on the estimation of multilevel pain intensity [36,37,39,41,42,44,45,48], and four studied both the detection of pain and the assessment of multilevel pain intensity [40,46,47,49]. Additionally, two studies proposed their automated detection model to differentiate between genuine and faked facial expressions of pain [38,43].…”