# Effects of Footpad Slope, Movement Direction and Contact Part of Foot on Foot-Based Interactions
## 4 Results
### Analysis of Pointing Errors  
A three-way analysis of variance was performed on the effect of the three independent variables on the pointing error distance. Figure 6 shows the average pointing error distance according to three independent variables. Among the three independent variables, two independent variables, the part of the foot in contact with the touchpad and the foot movement direction, significantly affected the error distance; foot contact part (F(2, 2146) = 124.26, \(p<0.001\)), foot movement direction (F(2, 2146) = 3.08, \(p<0.05\)), touchpad slope (F(1, 2146) = 2.83, \(p=0.093\)).  
The average error distance according to the foot part in contact with the touchpad was 7.05 mm in the case of contact using the big toe, 6.68 mm in the case of using the index toe, and 10.26 mm in the case of using the ball. As a result of the post hoc test by the Tukey test, there was no significant difference in the error distance when using the big toe and the index toe, while this value was shorter than when using the ball.  
The error distance according to the movement direction of the foot was 7.72 mm in the 0\({}^{\circ}\) direction, 7.97 mm in the 30\({}^{\circ}\) direction, and 8.32 mm in the 60\({}^{\circ}\) direction, and the error distance increased as the angle widened. The results of the ANOVA were significantly different depending on the angle (\(p=0.046\)), but the results of the post hoc test by the Tukey test showed no significant difference in the pointing error distance according to the movement direction.  
As a result of the analysis of the interaction effect between two factors in a row, a significant interaction effect on the error distance was between the part of the foot in contact with the touchpad and the slope of the touchpad (F(2, 2146 = 3.08, \(p<0.05\)) and between the direction of the foot movement and the slope of the touchpad (F(2, 2146 = 3.08, \(p<0.05\)). Figure 7 is a graph of the interaction that showed a significant interaction effect. In the interaction between the foot part contacting the touchpad and the touchpad slope, the ball part showed a longer error distance at the touchpad slope of 15\({}^{\circ}\) (10.466 mm) than at the touchpad slope of 7\({}^{\circ}\) (10.056 mm). On the other hand, in other parts (big toe, index toe), the error distance was shorter at the touchpad slope of 15\({}^{\circ}\) than the touchpad slope of 7\({}^{\circ}\).  
Looking at the interaction between the direction of the foot movement and the slope of the touchpad, we can see that the error distance was much shorter at the touchpad slope of 15\({}^{\circ}\) (7.758 mm) than that of the touchpad slope of 7\({}^{\circ}\) (8.891 mm) in the direction of 60\({}^{\circ}\). However, in other moving directions (0\({}^{\circ}\) and 30\({}^{\circ}\)), the error distance was similar regardless of the touchpad slope (7\({}^{\circ}\),15\({}^{\circ}\)).  
Figure 6: Main effects of the direction of foot movement (**left**), slope of foot touchpad (**center**) and foot part in contact with target point (**right**) on the foot pointing error.