Killed or Seriously Injured (KSI) is a standard metric for safety policy, particularly in transportation and road safety.
Killed: The usual international definition, as adopted by the Vienna Convention in 1968 is 'A human casualty who dies within 30 days after the collision due to injuries received in the crash'.
Serious injury: The definition is less clear-cut and may vary more over time and in different places. The UK definition covers injury resulting in a person being detained in hospital as an in-patient, in addition all injuries causing: fractures, concussion, internal injuries, crushings, burns (excluding friction burns), severe cuts, severe general shock which require medical treatment even if this does not result in a stay in hospital as an in-patient.
Slight injury: Sprain (including neck whiplash injury), bruising or cuts which are not judged to be severe. Also slight shock requiring roadside assistance.
The definitions used in the USA are as follows:
Fatal injury. To be used where death occurs within thirty consecutive 24-hour time periods from the time of the crash.
Incapacitating injury. Any injury, other than a fatal injury, which prevents the injured person from walking, driving or normally continuing the activities the person was capable of performing before the injury occurred. This includes: severe lacerations, broken or distorted limbs, skull or chest injuries, abdominal injuries, unconsciousness at or when taken from the crash scene, and unable to leave the crash scene without assistance. Does not include momentary unconsciousness.
Non-incapacitating evident injury: Any injury, other than a fatal injury or an incapacitating injury, which is evident to observers at the scene of the crash in which the injury occurred. This includes: lump on head, abrasions, bruises and minor lacerations. This does not include limping unless any actual injury can be seen.
Figures for fatalities are normally highly reliable in industrialised countries and few if any fatalities go unrecorded. Fatality figures are however often too low making it hard to see trends over time for one place.
Figures for the number of people seriously injured typically being an order of magnitude larger than the number of people killed and are therefore more likely to be statistically significant. However, classification of serious injuries is open to opinion, by medical staff or by non-medical professionals, such as police officers and may therefore vary over time and between places.
Figures for slight injuries are considered highly unreliable, largely due to under-reporting where injuries are self-treated.
