Figure 2b. (a) Scatterplot and (b) box plots for comparing regurgitation fractions measured at electron-beam CT with semiquantitative grades established at Doppler echocardiography. Crossbars in a delineate mean values of regurgitation fraction for each echocardiographic grade. Box plots show the medians, quartiles, ranges, outliers (
) (outliers are defined as values more than 1.5 box lengths away from the end of the box), and extremums (
) (extremums are defined as values more than three box lengths away from the end of the box). Horizontal lines in the box plots delineate thresholds of regurgitation fraction that best separate echocardiographic grades. There is a close relationship between the CT regurgitation fractions and Doppler echocardiographic regurgitation grades, with Spearman rank correlation coefficient of rs = 0.82 (P < .05).