Figure 3).

Bland-Altman plot showing the difference between manually scored portable sleep study-ApneaLink (PSS-AL, ResMed, USA) apnea-hypopnea index (AHI) and the polysomnography (PSG) AHI against the mean of the AHI values. The mean difference is ±3.9 events events/h. There are two outliers with a mean difference > ±2 SDs. One subject was awake for a significant proportion of the study, causing an overestimation of his AHI on the PSS-AL. The second outlier was a subject with sickle-cell disease who almost exclusively experienced hypopneas related to arousals rather than desaturations, accounting for the lower PSS-AL AHI (5.0 events/h) compared with PSG AHI (10.4 events/h). Dashed line represents ±2 SDs