I read with great interest the article by Briegel et al., recently published in Anesthsiology, in which the authors present a brilliant new method for noninvasive intermittent blood pressure monitoring. For validation, the authors compared a set of blood pressure data simultaneously measured using the new method and blood pressures recorded from a femoral artery catheter.

For further analysis of a total of 1,887 measurements recorded in 110 patients, Briegel et al. presented an analysis for clustered observations according to Bland and Altman. After their cornerstone paper in 1986, Bland and Altman have detailed their approach in several following papers.3,4  I would like to make some comments on the statistical approach used by Briegel et al. to compare the two methods.

First, a further reduction to a data set of five...

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