It is reasonable to advocate that the apnea-hypopnea index (AHI) is a clinically valuable metric for OSA because patients with a high AHI have a higher prevalence of excessive daytime sleepiness, hypertension, and cardiovascular disease than those with a lower AHI. Moreover, the contention that the AHI is a marker of disease is also sound given that clinical symptoms improve or resolve when the AHI decreases with treatment. However, these arguments only suggest that the AHI is, at best, a crude metric for OSA. Indeed, Dr Rapoport’s conclusion that the AHI is useful in defining the presence of OSA if severely elevated and that the risk of OSA is moderately increased indicates that the AHI is not a metric with high fidelity. A high-fidelity index of disease can identify the presence of that disease and exhibit a dose-response association with relevant health outcomes. The lack of a strong association between increasing AHI and clinical consequences, such as daytime sleepiness and hypertension, points to its relatively crude nature, and rigorous consideration of alternative or complementary measures that can correlate more precisely with end points than the AHI is required.