Sub-aggregations in Elasticsearch allow for the embedding of aggregations, both buckets and metrics, within other aggregations, enabling more refined and hierarchical data analysis. This powerful feature facilitates the continuous refinement of criteria groups, applying metrics at various levels to enhance the depth of reports. For example, by embedding buckets within buckets, users can determine the top contributing factors to incidents within different boroughs, enriching the original aggregation data with additional insights. Moreover, metrics, when used as sub-aggregations, can compute values based on documents within a bucket, such as calculating the total number of cyclist injuries in each borough. This combination of buckets and metrics offers limitless possibilities for data analysis, allowing for detailed reports on incidents by month, cause, and borough. These aggregations can be executed rapidly and update in near real-time, providing dynamic insights as new data streams in, showcasing the robust capabilities of Elasticsearch and its integration with Kibana for real-time data summaries and analyses.