Figure 2. A linear regression analysis for total power. The dark black line is the regression line through the data that results when the data points are treated as independent (n = 13). The correlation coefficient and the probability values of this linear regression are given. A significant linear relation is found, such that the increases in total power that occur with the different anesthetic levels correlate with the magnitude of the cerebral metabolic reduction caused by the anesthetics. Individual volunteers are labeled with “S numbers” for comparison among the various EEG descriptors. Some volunteers participated in all phases of the study (e.g., S2 and S3) and are shown on the graph as more than one data point. The nonindependent data points are joined together with lighter black lines. Because the data points are not completely independent, the correlation analysis should be interpreted with caution when the lighter lines do not approximately parallel the regression line.