# Location Optimization of Emergency Bell Based on Coverage Analysis for Crime Prevention
## 3 Materials and Methods
### Exploratory Data Analysis and Statistical Analysis
#### 3.3.1 Correlation Analysis  
In this subsection, a correlation analysis was conducted to identify significant variables associated with the major crime incidence index as a part of the EDA. Additionally, descriptions for each variable were described.  
Correlation analysis plays a crucial role in examining the relationships between different factors. By exploring these connections among variables, valuable insights into the decision-making process for selecting the ideal variable for bell location can be obtained.  
\[\begin{split} Major\;Crime\;Index=\frac{Number\;of\;five\;major\; crimes\;per\;each\;grid}{Total\;number\;of\;the\;five\;major\;crimes\;in\;Gwangju}\end{split} \tag{1}\]  
The National Police Agency categorizes the five major crimes as murder, robbery, theft, violence, and sexual harassment [30; 31]. Specifically, the major crime index was calculated by dividing the number of incidents of the five major crimes in each grid by the total number of the five major crimes in Gwangju.  
The focus was initially on the number of crimes occurring within each grid, enabling the calculation of the Major Crime Index, which reflects the grid-level crime situation in comparison to the entire Gwangju Metropolitan City. Subsequently, a correlation analysis was conducted among 27 variables to elucidate their relationships. However, 17 variables, including the Major Crime Index, were found to be statistically insignificant and were thus excluded from the analysis. The results indicated that ten variables were significantly correlated with a \(p\)-value of less than 0.05. Consequently, an in-depth investigation was carried out into the correlations among these 10 variables.  
The variable \"Num.CCTV\" represents the number of CCTV installations. The variable \"Num.Bell\" represents the number of emergency bell installations. The variable \"Float.pop.D\" denotes the sum of the transient population during daytime hours from 07:00 a.m. to 05:00 p.m. The variable \"Float.pop.N\" represents the sum of the transient population during nighttime hours from 06:00 p.m. to 06:00 a.m. The variable \"Pop.Woman\" stands for the total female population within the studied region. The variable \"Fac.Build\" represents the total number of buildings. The variable \"Num.Crime\" represents the total number of reported crimes. The variable \"Request.CCTV\" indicates the number of requests for the installation of additional CCTV systems. The variable \"Area.Building\" refers to the spatial extent of buildings within the study area. It was derived by summing up the spatial building area of each grid for administrative dongs. The variable \"Area.CCTV\" represents the coverage area or surveillance range of the installed CCTV systems. To determine the variable \"Area.CCTV,\" a 50 m buffer zone around each CCTV was created for each 100 \(\times\) 100 (m\({}^{2}\)) grid cell. The corresponding percentage coverage for the entire administrative dong was then calculated. This area of CCTV surveillance within each grid was then calculated using QGIS.  
As shown in Figure 2, these variables included the number of emergency bells (r = 0.6836); the transient population during the hours of 06:00 p.m. to 06:00 a.m. (r = 0.6706); the number of CCTV cameras (r = 0.6537); the transient population during the hours of 07:00 a.m. to 05:00 p.m. (r = 0.6338); the CCTV surveillance area (r = 0.6176); total population (r = 0.6104); total female population (r = 0.6104); the number of communual buildings (r = 0.5412); building area (r = 0.2019); and the number of requests for CCTV camera installations (r = 0.3132).  
It was observed that the correlation between the number of emergency bells and the number of CCTV cameras (r = 0.94), and the correlation between the number of emergency bells and the CCTV surveillance area (r = 0.94) were found to be very high. This could be attributed to the frequent installation of emergency bells alongside the CCTV cameras.