Receiver operator characteristics (ROC) curves for in-laboratory nasal flow respiratory disturbance index (NF RDI) in males and females for diagnosing OSA defined by polysomnography apnea-hypopnea index (PSG AHI) ≥ 5, panels (A) and (B), and for diagnosing severe OSA, defined as PSG AHI ≥ 30, panels (C) and (D), respectively