<p>The X-axis indicated (M<sub><i>max</i></sub> - M<sub><i>min</i></sub>) /2, namely M = 12.78, as cut-off point. The Y-axis indicated the <i>coefficient b</i> in the regression analysis, whose <i>P</i> values of difference-test greater than 0.05, are set as 0 in the figure, and (12.78, 0) was set as the origin of the quadrant.</p