Receiver operating characteristic (ROC) analyses for DSHB (green dotted line), DSEM (red dotted line), DSAC (pink dotted line), MMS (solid blue line), TMD (cyan dotted line), and IIG (solid brown line). Cormack-Lehane grading of glottis exposure over II was considered the threshold of difficult laryngoscopy during the study. Black dotted line=reference line. DSHB: the minimum distance from skin to hyoid bone; DSEM: the distance from skin to epiglottis midway between the hyoid bone and thyroid cartilage; DSAC: the minimum distance from skin to anterior commissure; MMS: modified Mallampati score; TMD: thyromental distance; and IIG: interincisor gap.