Patient notes and clinical journal entries from multiple patients are compiled into a study. What type of study is this?

A case series is a descriptive study that collects and presents data from a group of patients with similar characteristics, diseases, or exposures. It has no control group and no randomization - it simply documents what was observed in a series of cases. Case series are useful for describing the natural history of rare conditions, identifying patterns, and generating hypotheses for future research. They rank low on the evidence hierarchy but were historically important (e.g., the first descriptions of HIV/AIDS were case reports and series). A single patient's notes would constitute a case report.