Fig. 5. Bland–Altman plot displaying the difference between Bispectral Index (BIS) and Patient State Index (PSI)  versus their arithmetic mean, based on 11,000 values obtained in 22 patients. The linear regression line between difference and arithmetic mean is shown as a  solid line , and its 99% confidence interval is shown as  dashed lines .For illustrational reasons, the ordinate was scaled from −20 to +20 even though some data points were outside this range.