The contingency table of visually scored polysomnographic classification (‘R&K’) versus the classification by IDOS index for the combined epochs of all 15 datasets is shown. The amount of the epochs classified as either wake, non-SWS or SWS are given for both methods. Rows represent the number of epochs scored as each state by conventional visual analysis according to R&K. Columns represent the classification of the same epochs by the IDOS index. The agreement for three classes was excellent (Cohen’s kappa coefficient = 0.82, SD = 0.06), agreement for two classes was slightly better (kappa = 0.84, SD = 0.09). IDOS, ICU Depth of Sleep; R&K, Rechtschaffen and Kales; SD, standard deviation; SWS, slow wave sleep.