Final answer:
An unusual aggregation of health events in space or time is known as a disease outbreak, which is extensively studied in epidemiology to understand patterns of incidence and measures of association.
Step-by-step explanation:
An unusual aggregation of health events grouped in space or time refers to a disease outbreak. This is an event in which two or more people contract an infectious disease from a common source of infection. To understand and control outbreaks, epidemiologists study patterns of incidence and measures of association, comparing disease rates among different groups and identifying potential risk factors. Spatial relationships may also indicate causality, for instance, when an increase in air pollution correlates with a rise in lung cancer cases in the same area.