Emerging technology reviewAssessment of Trending Ability of Cardiac Output Monitors by Polar Plot Methodology
Section snippets
Methods
A number of steps were required to transform the X-Y ΔCO data into polar data, and these steps are presented later (Fig 1). Statistical variables that assessed trending ability and described the polar plot needed to be identified. In Bland and Altman analysis, the bias and limits of agreement are used to assess agreement.3 The following variables based on the polar plot and polar angle (θ) were chosen: (1) the mean polar angle (or angular bias) and (2) 95% CIs (limits of radial agreement) of
Results
A total of 18 articles with 4-quadrant plots were identified, 2 of which were excluded because the range of values of the data was too small for polar analysis.21, 22
Discussion
Polar plots present the data from a 4-quadrant plot in a similar format to a Bland and Altman plot but with a radial distribution of data points about a polar origin3 (Fig 2). Full- and half-circle formats can be drawn. The bias becomes the mean of the polar angles formed by these data points and reflects the difference in calibration between the reference and test methods. The radial limits of agreement replace the horizontal limit lines in the Bland and Altman plot. A modified concordance
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