A system is disclosed wherein patient data, such as an electrocardiogram (“ECG”) signal or a chest impedance measurement signal, collected by a defibrillator device during a resuscitation event is analyzed and processed by a computing device to provide an assessment of CPR administered during the event. The CPR assessment results in one or more CPR figures of merit that relate to temporal characteristics of the CPR relative to the duration of the event. In one embodiment, the CPR figure of merit represents a percentage of the event period during which chest compressions were administered to the patient.