Bispectral index and state entropy of the electroencephalogram during propofol anaesthesia

Editor—We read with interest the study by Bonhomme andcolleagues,¹ in which some interesting differences from ourpublished data² have emerged. We agree that Bland–Altmananalysis appears to be the right statistical test to performin an attempt to determine the degree of agreement between twomeasurement techniques. The only two studies that used the Bland–Altmananalysis to compare BIS and SE have been published by Bonhommeand our group. We found a good comparability (mean difference0.1) between the two (the upper and lower limits of agreementwere –19.9 and 19.6). Bonhomme used the same type of analysison data pairs averaged over 1 min over the entire period andreported a mean difference of 2.5 and similar upper and lowerlimits of agreement (–19.5 and 24.6). We agree that thismay be