Which study design is, by definition, an interventional study?

In an interventional study the investigator actively assigns or manipulates the exposure or treatment. This is the defining feature of an experimental study such as a randomized controlled trial.Other options: Cohort, case-control, and cross-sectional designs are observational; the investigator measures but does not assign the exposure.Key exam takeaway: Interventional = the researcher controls the exposure (experimental). All other listed designs are observational.