A-C, Examples of the categorical photographic variables. (A) Modified Mallampati score: Representative examples of each modified Mallampati class obtained from photograph P1 are shown. Class I indicates full visibility of the uvula and tonsillar fossa. Class II indicates visibility of the upper portion of the uvula and partial visibility of the airway. Class III indicates visibility of the hard palate and base of the uvula. Class IV indicates visibility of the hard palate and no visibility of the soft palate. In addition to modified Mallampati scores, we derived a measure of airway visibility using these photographs; the airway is visible in Class I and Class II, but it is not in Class III and Class IV. (B) Tongue ridging. Representative examples of the absence of ridging and evidence of ridging (black arrows) are shown, from photograph P1, P2, or P4. If evidence of tongue ridging is visible in any frontal intraoral photo, subjects are then graded for presence of tongue ridging. (C) Pharyngeal narrowing. Representative examples of each grade of pharyngeal narrowing are shown, from photograph P1, P2, or P4. Grades are based on the location of the intersection between the palatopharyngeal arch and the tongue, relative to tongue width. Grade 1 indicates that the arch intersects at the edge of the tongue. Grades 2, 3, and 4 indicate that the palatopharyngeal arch intersects at 25%, 50%, and 75% or more of the tongue width, respectively.