Crime and justice statistics

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 incidence and effects of crime in the community. The sources used to compile this edition are listed in the References section.

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 have the advantages of covering the whole population that comes into contact with the criminal justice system and of remaining relatively stable in their collection and production over time.

There are limitations to these data, however, including comparability among agencies and jurisdictions. Most of the data have been collated at a national level only relatively recently, if at all: 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 much has improved, definitions and collecting methods are not always uniform among 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 detail 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 of 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. 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 are also expensive, so they tend to be one-off or infrequent. Surveys used in preparing this year's edition include the Personal Safety survey, the Crime and Safety survey, and the Personal Fraud module, all 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 re-classified as manslaughter, or there may be insufficient evidence to convict an alleged offender in any criminal case.

Apparent marked relative fluctuation in crime rates may be due to the small numbers involved. For example, from four homicides in one year, alteration by one homicide per year will appear as a 25 percent change.

Because of rounding, some percentages may not sum to 100.

Rates are determined against one of two different types of base population—either the total population or the relevant population. The property crime victimisation rate, for example divides the number of property victims by the total population. In this publication, data in relation to the total population are presented as per 100,000. Rates in relation to a relevant population group refer to the number of persons as a proportion of that population group (for example, juveniles, males, females, or Indigenous persons).

Population projections for Indigenous adults are based on data provided by the Australian Bureau of Statistics (ABS). The ABS uses two methods to estimate Indigenous populations: the low series and the high series. Both employ certain assumptions about births, deaths, and migration. Figures in this publication are based on high-series population data. This method accounts for the effects of increasing propensity to identify as Indigenous from the 1991 to the 2001 censuses. In 2004, the ABS released revised Indigenous population figures in the high series for 2001-03, based on the 2001 census. Rate calculations for these years therefore differ from those in some previous publications.

Data on juveniles refers to persons aged 10 to 17 years, and adults to persons aged 18 years and older. Issues of Australian crime: facts & figures up to 2004 defined adults as persons aged 17 years and older, affecting calculations such as rates of imprisonment. From the 2005 issue onward, imprisonment rates were recalculated based on the revised adult age and will thus differ from those quoted in older issues.