Figure 1. Total sleep time disagreement between measurements.

Bland-Altman concordance between total sleep time as measured by PSG and the S+ device (A) or actigraphy (B). Solid lines indicate average discrepancy, dashed and dotted lines indicate ± 1 standard deviation, and symbols correspond to the number of minutes differing for each participant. On the ordinate, a positive difference indicates overestimation and a negative difference underestimation relative to PSG. The range of participant sleep time in minutes, according to RPSGT-scored PSG, is on the abscissa. Act = actigraphy, Avg = average, Diff = difference, PSG = polysomnography, S+V1 = algorithm version 1, S+V2 = algorithm version 2, SD = standard deviation.