The steepness of the slope reflects the importance of each effect, From the graphical results in Figure 8.12, it is apparent that the most important effects are factor A and the AC or BD interaction. Since AC is aliased with BD, we must go back to the definition of the factors to determine which interaction is most likely responsible for the steep slope in Figure 8.12. Since it is highly unlikely to have a “tire pressure x type of oil” interaction (AC), it is concluded that the steep slope in Figure 8.12 is due to the BD, or “timing x type of gas,” interactions. The BD interactions graph is shown in Figure 8.13. Notice that the large star,…, is plotted as the average y when B = 1 and D = 1, i.e., the average response values for runs 3 and 8 which is computed as follows: