Termin index event używany jest bardzo często nie tylko w medycynie i jest tłumaczony zależnie od kontekstu.

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"The Time of Entry to the Study: In nonrandomized studies, a standardized definition of the time of entry into the study ("time zero") is important to avoid selection bias and to facilitate meaningful comparison between various studies." Ideally, the time of entry should be the index event of ventricular tachycardia or cardiac arrest. The index event is the arrhythmic episode that begins the therapeutic process resulting in the implantation of the ICD(Implantable cardiac defibrillator), administration of medication, or other intervention specific to managing or preventing the recurrence of the index event. For reporting ICD patient outcomes, an alternative entry time may be the time when the decision to implant an ICD is made. A signed consent form is a documentation of this decision but may underestimate the waiting period (see Definitions). It may be desirable to report outcomes using two reference points, i.e., the index event and the time when the decision to implant an ICD was made for easier comparison of different studies. Fatal events during the waiting period should be reported as waiting period deaths".