Figure 3: Similarity measures for the obtained coupling fuctions.
From: In vivo cardiac phase response curve elucidates human respiratory heart rate variability
Box–whisker plot illustrates the correlation coefficient ρ (a) and the difference measure η (b), for all available pairs of functions (high similarity corresponds to large ρ and small η). ES: similarity between the functions Qe (respiration—ECG) of the same subject, obtained from two trials; it is maximal. EG: similarity between Qe of different subjects in the group demonstrates low interpersonal variability. PS and PG: intra- and interpersonal similarities for Qp (respiration—arterial pulse). EPS and EPG: intra- and interpersonal similarities between Qe and Qp. Notice that the correlation can be maximized by computing it for phase-shifted functions; so, for example, the outlier value in (a) ES, at ≈0.6 becomes as high as 0.9. This phase-shift might reflect a variation of internal delays and therefore might have a physiological meaning; however, this issue requires a separate study. The number of cases used for computation of the six box plots is (from left to right): 11, 18, 29, 314, 172 and 491. (The low border of the box, the red line, and the upper border are the first, second and third quartiles, respectively. The whisker length is 1.5 times the interquartile range.)
