From CpapWiki
AHI RAI Scale
AHI/RAI Scale is a measurement of both the Apnea/Hypopnea Index (QHI) and the Respiratory Arousal Index. If a person has less than 5 events per hour then that person's AHI/RAI would be 0 and that person would not have apnea. 5 -15 events/hour = (mild); 15-30 events/hour = (moderate); >30 events/hour = (severe).