Observational study

An observational study is a type of clinical research in which investigators assess health outcomes in groups of participants without assigning an intervention: treatment, if any, follows normal clinical practice and the decision to prescribe is independent of the decision to include the patient in the study. Main designs are cohort studies (following exposed and unexposed groups forward), case-control studies (comparing exposure histories of people with and without an outcome) and cross-sectional studies (measuring exposure and outcome at one point in time). Registries and natural history studies are observational.

In the EU, observational studies of medicinal products are non-interventional studies falling outside the Clinical Trials Regulation and governed by national law and, for post-authorisation safety studies (PASS), by the pharmacovigilance legislation and the EMA's GVP Module VIII. They are a major source of real-world evidence for regulators, HTA bodies and payers, and are increasingly conducted using electronic health records, claims databases and health data warehouses.

Observational studies process health data, frequently through secondary use of existing records without direct contact with patients. Under the GDPR this requires a research legal basis (Art. 6(1)(e) or (f) with Art. 9(2)(j)), appropriate safeguards under Art. 89, and attention to the information duty under Art. 14, which may be fulfilled through general notices where individual information is impossible or disproportionate. National frameworks such as France's MR-004 (studies not involving the individual) set specific conditions, and the European Health Data Space will provide a harmonised access route from 2029.