• Bernd Saugel, Oliver Grothe, and Julia Y Wagner.
• From the *Department of Anesthesiology, Center of Anesthesiology and Intensive Care Medicine, University Medical Center Hamburg-Eppendorf, Hamburg, Germany; and †Department of Economic and Social Statistics, University of Cologne, Cologne, Germany and Institute of Operations Research, Karlsruhe Institute of Technology, Karlsruhe, Germany.
• Anesth. Analg. 2015 Aug 1; 121 (2): 514-24.

AbstractWhen comparing 2 technologies for measuring hemodynamic parameters with regard to their ability to track changes, 2 graphical tools are omnipresent in the literature: the 4-quadrant plot and the polar plot recently proposed by Critchley et al. The polar plot is thought to be the more advanced statistical tool, but care should be taken when it comes to its interpretation. The polar plot excludes possibly important measurements from the data. The polar plot transforms the data nonlinearily, which may prevent it from being seen clearly. In this article, we compare the 4-quadrant and the polar plot in detail and thoroughly describe advantages and limitations of each. We also discuss pitfalls concerning the methods to prepare the researcher for the sound use of both methods. Finally, we briefly revisit the Bland-Altman plot for the use in this context.

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