During a sleep study, the total number of hypopneas (defined as partial flow limitation or collapse) and apneas (total flow limitation or collapse) are divided by the number of hours of total sleep time. The AHI is reported in number of events per hour. For adults, normal is 0-4 events/hour. Mild OSA is defined as 5-14 events/hour. Moderate OSA is 15-29 events/hour and severe is 30 events/hour and above.