Fig. 1

Patient subgroups (flowchart). The objective is to identify those patients that were registered for EFFECT by the participating centers, and those that were not but also should have been. First, based on EFFECT data, the study population was categorized in patients registered and not registered for EFFECT. Next, within the group of non-registered cases, a further distinction was made based on whether main treatment was performed in an EFFECT-participating center and, if yes, whether the patient’s incidence date falls inside the hospital’s active registration period. This way, four patient subgroups were defined: (a) patients registered for EFFECT by the participating centers (Registered EFFECT-Patients; REP); (b) non-registered patients that underwent their main treatment during a participating center’s active registration period, and therefore also should have been registered (Non-Registered EFFECT-Patients; Non-REP); (c) non-registered patients that underwent their main treatment outside of a participating center’s active registration period, and therefore could not have been registered (Non-EFFECT-A); and (d) non-registered patients that underwent their main treatment in a non-participating center, and therefore could not have been registered (Non-EFFECT-B). A participating center’s active registration period was determined by chronologically ranking all its registered cases based on their incidence date, and defined as starting from the first until the last incidence date