Figure 3. Extent of agreement among the seven scoring sessions when a given sleep stage is scored at least once in one of the sessions.

W, stage awake; REM, rapid eye movement sleep; N1, N2, and N3 are nonrapid eye movement stages 1, 2 and 3. Note that when stage awake occurred in one scoring session there was unanimous agreement (7/7) about the stage in 65 % of cases. A similar behavior was seen in stage REM. However, when either N1 or N3 was scored there was unanimous agreement in only a small fraction of the epochs, whereas in more than half the cases the score was seen in only one or two other sessions. Diagonal lines are the cumulative occurrences. Vertical bars are standard deviation. n, number of epochs in each category.