A Comparative Analysis of Methods for Evaluation of ECG Signal Quality after Compression

Figure 6

Illustration for calculation of sensitivity and variability (standard deviation in a statistical sense of meaning). Normalized curves for all 15 leads are the thin colour lines; average curve calculated from the 15 curves is the thick black line. The blue frame zooms on an important part of the graph for the area around the important avL limit of 0.8 bps. In this frame, the calculation of sensitivity and variability is illustrated. Sensitivity (highlighted in green) is calculated from the average curve as an absolute value of a difference of its values at avL = 0.75 bps and avL = 0.85 bps (marked by green crosses). Sensitivity is an approximation of the derivative of the curve at avL = 0.8 bps (approximation of the slope of the tangent line to the curve at that point). The area from which the variability is calculated is defined by the dashed red line delimited by two red crosses. From the points of all 15 curves at avL = 0.8 bps (defined area), the standard deviation in a statistical sense of the meaning is calculated.