Difference between location parameters of the V_trail − V_lead distributions as a function of the WT. The three quartiles and the mean values during the minimum and two phases of solar cycle 23 are marked by different colors. The size of the circles depends on the probability given by the sign test as: probability ≤0.15 (small), 0.1 (medium), and 0.05 (large), i.e., when the null hypothesis (H₀: ) is rejected at the 15, 10, and 5% level based in the sign test. The events considered in each subset with probability ≤0.05 are also shown in the lower right panel.