Statistically, I don't have an exact number. However, in my dental practice I'm looking at the child's face growth (lower jaw can be delayed in growth because of open mouth breathing), their eyes (for venous pooling under the eyes), I ask about bedwetting, attention during the day (children can be mis-diagnosed with ADHD that have obstructive sleep issues), snoring, grinding their teeth, issues with allergies, mouth breathing, cognitive delay or learning issues, and if the parent witnessed the child gasping for breath, or observation/listening to their child stop breathing. I visualize the tongue, throat (tonsil size), I watch the child for mouth breathing, and I hold each nostril closed, as the child breathes out of the nose, each side, fogging up the mirror (I call it the "blowing boogers on my mirror test"...all the while asking questions and listen to the parents answers. In my education process, I am taught that even ONE apneic episode in an hour warrants a sleep study, and that is what I advise my parents at the child's dental appointment. If you have other questions, please ask.