National crime statistics provide comparable data across the states and territories for selected crimes recorded by state and territory police in Australia.
Two sources of national statistics provide a picture of crime in Australia: crimes recorded by police, and crime victimisation surveys. Crimes recorded by police relate to victims of criminal incidents who have become known to police and whose experiences have been recorded by police. These offences may have been reported by a victim, witness or other person, or they may have been detected by police. These statistics do not provide a total picture of crime, as not all crimes come to the attention of police. In addition, care should be taken in interpreting police statistics, as fluctuations in recorded crime may be a reflection of changes in community attitudes to reporting crime, changes in police procedures or resources, or changes in crime recording systems, rather than a change in the incidence of criminal behaviour. Significant events occurring in particular years may also contribute to fluctuations in recorded crime.
A complementary picture of the nature and extent of crime comes from crime victimisation surveys. These household-based surveys collect information on individual's experiences of selected crimes and whether or not they reported the crimes to the police. Crime victimisation surveys are suitable for measuring crimes against individuals (or households) who are aware of and recall the incident and how it happened, and who are willing to relate what they know. Crime victimisation surveys allow crime information to be related to personal and household characteristics, and facilitate the study of patterns of victimisation over time and across crime categories.
Not all types of crime are suitable for measurement by household surveys. No reliable victim-based information can be obtained about crimes where there is no specific victim (e.g. trafficking in narcotics) or where the victim is deceased (e.g. murder). Crimes of which the victim may not be aware cannot be measured effectively; some instances of fraud and many types of attempted crimes fall into this category. It may also be difficult to obtain reliable, comprehensive information about certain types of crime, such as sexual offences and assaults by other household members. Finally, no reliable data can be collected by household surveys on crimes against commercial establishments.