b"CARES 2022 Annual ReportData Linkage: Maximizing the Value of Public Health DataThere are numerous entities in the United States responsible for creating and maintaining health records, including government agencies and private institutions, as well as individual researchers. The use of data silos - where data is created, stored, and analyzed in separate systems - is common. However, this fragmentation of data presents challenges in answering critical public health questions. To facilitate high-quality research and evaluation, it is important to integrate datasets and gather information from various secondary data sources, such as environmental and social data, to gain a more comprehensive understanding of the complex factors that influence out-of-hospital cardiac arrest (OHCA) and overall public health. The variables collected by CARES, such as geographic information, and patient information, such as age, sex and date of arrest, allow for robust linkage of registry data with other datasets, enabling researchers to answer questions regarding OHCA not readily available. One method of matching records from separate databases is to use the deterministic method', where unique identifiers are used for linkage. However, it is not always possible to directly link records due to insufficient identifying information or concerns related to confidentiality. In such situations, probabilistic matching, which uses a statistical approach to measure the likelihood that two patient records represent the same person, can be applied.Urbanicity Data Linkage The CARES dataset is geocoded on an annual basis and linked to a number of census-tract level variables including median household income, poverty status, urbanicity, and educational attainment. By analyzing data linked to census-level information, researchers were able to investigate the impact of bystander cardiopulmonary resuscitation (CPR) and automated external defibrillator (AED) use on survival rates across urban and rural settings. Despite a higher proportion of arrests that were witnessed and received bystander interventions within non-urban areas, OHCAs which occurred in suburban, small town, and rural areas had poorer clinical outcomes than urban and large rural areas (Table 1). This study emphasized that the likelihood of receiving bystander interventions and the probability of favorable clinical outcomes after OHCA differ across the urban-rural spectrum. By tailoring intervention strategies to the unique needs of each community, including addressing challenges related to urban-rural differences in care and outcomes, we can strive to improve OHCA survival rates and clinical outcomes in all settings. Table 1. Outcomes of the study population in areas along the urbanrural spectrum.Figure used with permission of Elsevier from Grubic, N et al. Bystander-initiated cardiopulmonary resuscitation and automated external defibrillator use after out-of-hospital cardiac arrest: Uncovering disparities in care and survival across the urban-rural spectrum. Resuscitation. 75:150-158 (2022). Permission conveyed through Copyright Clearance Center Inc. Environmental Data Linkage Linking CARES data with environmental data allowed researchers to assess the association of acute exposure to ambient air particulat e matter and ozone with risk of OHCA. Data from the CARES registry was combined with ambient air temperature data retrieved from the North American Regional Reanalysis using the deterministic method, linking by zip code. Malik et al. found that exposure to higher levels of ambient air ozone on day of arrest, but not particulate matter 2.5 m (PM 2.5 ), was associated with a higher risk of cardiac arrest (Figure 1). The results highlight the importance of understanding the dose-response relationship of ozone with risk of OHCA to inform policy on monitoring ambient air levels in the U.S.44"