Because STATS19 crash data is collected by police officers and staff rather than health professionals, severity does not provide a precise medical definition of injury.
Severity is defined by STATS20 as falling in one of three possible categories:
- Fatal injury includes any cases where death occurs within 30 days as a result of as a crash. It does not include death from natural causes or suicide.
- Serious injury includes (but is not limited to): fracture, internal injury, severe cuts, crushing, burns, concussion and fatalities occurring 30 or more days after the crash. Serious casualties are often (although not necessarily) detained in hospital for treatment.
- Slight injury includes (but is not limited to): sprains, whiplash, bruises, slight cuts and slight shock requiring roadside attention. Slight casualties can often (although not necessarily) be treated at the roadside.
Since 2012 many police forces have adopted new reporting systems for recording casualty information, most notably the Collision Reporting And SHaring system (CRASH). In contrast to previous practice, which required police officers to make personal judgements concerning injury severity, CRASH incorporates a more detailed and accurate method for injury classification.
The Department for Transport has concluded that this change has resulted in an increase in the number of injuries reported as Serious across Britain. For this reason users of serious injury road casualty statistics (including those described as KSI) should be interpreted with caution. The support MAST users in using these statistics appropriately, the Reported by Police Force with CRASH dimension can be used to distinguish between crashes and collisions reported in CRASH and those reported using more traditional methods.
The severity of a crash is defined as the highest severity of injury suffered by any resultant casualty. Consequently, it is meaningful to refer to a slight casualty which was suffered as a result of a serious crash, but not vice versa. This can sometimes lead to misunderstandings when severity information is reported.
Crash Severity can be shown as a separate dimension in any report based on Crashes, Vehicles or Casualties. It should not be confused with Casualty Severity, which is shown only in reports based on Casualties.
Particular care should be taken with this issue if the Crash Casualties Count measure is used in crashes reports.
The term KSI
It is common practice to group fatal and serious casualties together for analysis purposes. Such information is often described by the abbreviation KSI casualties (short for 'Killed or seriously injured'). It is also common practice to group fatal and serious crashes together for analysis purposes. Such information is often described by the abbreviation KSI crashes.
Severity in MAST
Severity is represented in MAST by a hierarchy with two levels. The upper level contains KSI and slight, with the lower level distinguishing between fatal and serious. The same hierarchy is used to describe both casualty and crash severity.