# Calculation of the Rearfoot Angle Representing Flatfoot from Comparison to the Cavanagh Arch Index
## 3 Results
### Correlation Results between Subject Characteristics and [PERSON]'s AI  
This study was conducted to examine an alternative RFA measurement to determine flatfoot by using the correlation between Cavanagh's AI and RFA. Prior to the correlation between AI and RFA, a correlation between subject characteristics such as foot size, gender, BMI, FW, FL, FAC, and Cavanagh's AI were analyzed and the result is presented in Figure 4.  
Figure 4 shows the correlation between variables presented in Table 1 and the average AI. There is no difference between the AI mean of left and right feet. This indicates that most of the subjects were standing upright during the footprint scanning. The average AI of the female is greater than male, which is about 0.04. The range of AI values is 0.27-0.44, with AI median values being approximately 0.35. There are several subjects consisting of 2 males and 5 females with AI \(\geq\) 0.4, and others are categorized as over-pronation category (AI \(>>\) 0.26) [4].  
According to Table 1, the average BMI of males is greater than females, which is also similar to the result presented in [23]. Meanwhile, from BMI grouping, the average AI of the overweight category is larger than the normal category, i.e., 0.38 \(\pm\) 0.06 and 0.35 \(\pm\) 0.05, respectively, as presented in Figure 4 [24].  
The mean FL and FW on the sole of the left and right feet for all subjects are almost similar. This indicates that most of the subjects were standing upright during the footprint scanning. The mean FL of males is greater than females [20]; however, the FL \(\geq\) median values show that the average AI is much larger than FL \(<\) median (median value of all subjects is 235.3 mm), as presented in Figure 4. It means that a large FL affects the degree of flatfoot.  
The average FW of males is higher than females [25] but differs only around 0.9 mm. The average AI for FW \(\geq\) median and FW \(<\) median values for all subjects are approximately the same, i.e., 0.35 \(\pm\) 0.04 and 0.35 \(\pm\) 0.06 (median = 95.2 mm, as presented in Table 1). This means that a large FW does not affect the degree of flatfoot, as presented in Figure 4.  
Typically, in the range of FAC values of males and females, it shows that the sole shape of the male foot is larger than the female [20]; however, the present study revealed that the  
Figure 4: The correlation between the foot size, gender, BMI, and foot dimension parameter to the average AI.  
females have a larger correlation to [PERSON]'s AI than the males. This indicates that the shape of the foot does not have a direct correlation to the flat foot.  
According to [26], there is a significant correlation between BMI and FAC, with a correlation coefficient of 0.75. This shows that the higher the BMI value, the greater the FAC value; however, there is no significant correlation between FAC and AI in the present study, as presented in Figure 4. Overall, there is no significant correlation between subject characteristics and [PERSON]'s AI for all parameters, i.e., foot size, gender, BMI, FW, FL, and FAC, as the correlation is lower than 0.4, as presented in Figure 4. This indicates that these parameters have a small correlation with [PERSON]'s AI. The highest correlation shown is BMI, especially in the overweight category, with a correlation of 0.38. The correlation between female gender and [PERSON]'s AI, as well as the FL < Median and [PERSON]'s AI, show slightly less than overweight BMI of about 0.37. In contrast, the correlation between male gender and [PERSON]'s AI, as well as the correlation between FL \(\geq\) Median and [PERSON]'s AI, is the smallest at about 0.33. This indicates that males have less probability of flatfoot than females.