Registry linkage is a research method that involves combining data from multiple registries or databases to create a comprehensive dataset for analysis. This method allows researchers to gain deeper insights into complex health issues by linking various sources of data, such as medical records, disease registries, and administrative databases. By merging these datasets, researchers can examine relationships between different variables and identify trends or patterns that may not be apparent when analyzing single datasets in isolation. Registry linkage is particularly useful in longitudinal studies or studies that require large sample sizes, as it allows researchers to access a wealth of information from multiple sources. However, there are challenges associated with registry linkage, such as ensuring data privacy and security, as well as using consistent definitions and coding procedures across different databases. Overall, registry linkage is a valuable research tool that can help advance our understanding of health and disease.