# A Visual Analytics Framework for Inter-Hospital Transfer Network of Stroke Patients
## 3 Analysis of Data and User Task
### Hospital and Patient Transfer Data  
In the Republic of Korea, the HIRA (Health Insurance Review and Assessment service) accumulates and manages a list of hospitals registered as treatment institutions for specific diseases, as well as the data related to patient transfers between hospitals, their treatment processes, and outcomes. The data used by medical researchers who conducted the joint study consisted of the transfers of 19,113 stroke patients among 1009 hospitals from 1 July to 31 December 2016. The data used in this study are summarized in Table 1.  
Figure 1: Exploratory visual analysis framework for stroke patients (PatientFlow). Some data needed to be preprocessed before analysis, and parts of the provided data were anonymized to prevent the hospital's or personal information from being identified. For example, the detailed address information that can specify a hospital in the hospital list data is not provided, and only the regional administrative district (e.g., cities and provinces) and second-level administrative district (e.g., cities, counties, or districts) information are provided. The hospital ID is also randomly assigned to prevent the name of the hospital from being identified. Accordingly, the GPS coordinates of the government office (e.g., city hall, county office, or ward office) of the relevant administrative districts are used instead of the actual location of the hospital to display the location of the hospital on a map. In this case, random jittering is applied in the process of rendering on the screen to distinguish them on a map because multiple hospitals within the same administrative district can overlap. The distance between hospitals is calculated as a straight-line distance based on the GPS coordinates before jittering is applied. Other data about the hospital include classification based on the size of the hospital (e.g., A = quaternary hospital, B = tertiary hospital, C = secondary hospital, and D = primary hospital). One can also classify the hospital based on the stroke care hospital (SCH) designation status. An SCH is a hospital equipped with healthcare professionals and an environment that can provide intensive treatment, including EVT, for stroke patients; the SCH designation status is considered important in the network analysis process in previous related studies. Based on the data received from the HIRA, all quaternary hospitals are designated as SCHs, and some tertiary hospitals are designated as SCHs. None of the secondary or primary hospitals are designated as SCHs. Accordingly, the interface is configured to facilitate the classification of B-type hospitals depending on their SCH designation status in the analysis process (Section 4.4). We complied with restrictions on the confidentiality of data: patient transfer data only provides the sum of the number of patients transferred between hospitals to prevent the identification of individual patients. The data contains the ID number of each hospital and the number of patients transferred in and out. Among the types of patient transfer, those discharged after receiving treatment at the first hospital visited (stay), and those transferred to another hospital without receiving treatment at the first hospital visited and discharged after receiving treatment at the transferred hospital (transfer and stay) are examined. In practice, there are other cases where patients receive treatment at the first hospital and are discharged from the transferred hospital. The last case involves three hospitals where patients are transferred from the first hospital to the second hospital to receive treatment and then transferred to a third hospital to get discharged. As such cases account for about