Self-controlled case series study (SCCSS) is a novel strategy to control between-person confounders by comparing the risk and reference periods in each patient. SCCSS investigates the association between transient exposure and an adverse event. It was developed to study adverse reactions to vaccines. Risk periods are defined during or after the exposure. Then the method finds a relative incidence i.e. the incidence in risk periods relative to the incidence in control periods. This editorial describes the definition, origins, design, assumptions, advantages, and limitations of this research method.
