Statistics used in Australian crime: Facts & figures come from a variety of sources. There are two types of data collections, administrative and survey, and both types of information are needed to help inform our understanding of the level and effects of crime in the community. The sources used to compile this issue are listed in the references.
Administrative collections - Criminal justice agencies keep records of their workflow at different stages. For example, police keep incident records, courts record the details of cases and their disposition, and corrections agencies have details of the offenders in their charge. Most basic information comes from these administrative collections, which cover the whole population that comes into contact with the criminal justice system, and remain relatively stable in terms of collections and production over time.
There are limitations to these data, however, including comparability across agencies and jurisdictions. Most of the data have been collated at a national level only relatively recently - recorded crime from police records since 1996, prisoners since 1983, and all criminal courts since 2001. There are as yet no national data on offenders. The collections are not all based on the same unit of measurement; for example, police record details about offences, courts record cases, and corrections agencies record information about individual prisoners.
Although there has been much improvement, definitions and collecting methods are not always uniform across jurisdictions, and recording quality may be an issue. It can take time to reach agreement at a national level on key issues including definitions of new and emerging offences. More detailed information about crime and justice is often available at a jurisdictional level, even when it is not possible to produce national statistics.
Not all crimes are reported to police - this is believed to vary from a low of 20 percent for sexual assaults to a high of 95 percent for motor vehicle thefts. This is one of the main reasons that the other main type of data collection, surveys, is undertaken.
Surveys - Crime victimisation surveys have the advantage of asking the same questions in the same way across the whole of the sample population. These answers are then recorded in a similarly uniform way so that the information they provide is reliable and comparable.
Crime victimisation surveys are believed to provide a more accurate picture of actual crime rates in society. Surveys are expensive, however, so they tend to be either one-off or infrequent. It is not always valid to extrapolate from a sample to the whole population, however, and all sample surveys have a certain amount of error. Surveys used in this publication this year include the Personal safety survey and the Crime and safety survey, both conducted by the Australian Bureau of Statistics.
Notes on using these statistics
It should be noted that police information on victims and offenders has not been tested in court. A murder as recorded by police might later be reclassified as manslaughter; there may be insufficient evidence to convict an alleged offender in any criminal case.
Where crime rates appear to fluctuate markedly, this may be due to small numbers involved. For example, where one jurisdiction records four homicides in a year, one more or less the next year will appear to be a 25 percent change.
Because of rounding, some percentages may not sum to 100.
Rates are determined against two different types of base population - either the total population or the relevant population. The property crime victimisation rate, for example, divides the total population by the number of victims of property crime. In this publication data are presented as per 100,000 population where the total population is used. Rates per relevant population refer to the number of persons as a proportion of a specified population group (for example, juveniles, males or females, or Indigenous persons).