DATA QUALITY: SURVEY DATA
RELIABILITY OF THE ESTIMATES
1 Since the estimates from the Crime Victimisation Survey are based on information obtained from a sample of persons, they are subject to sampling variability. That is, the estimates may differ from those that would have been produced had all persons been included in the survey.
2 One measure of the likely difference is given by the standard error (SE), which indicates the extent to which an estimate might have varied by chance because only a sample of persons was included. There are about two chances in three (67%) that a sample estimate will differ by less than one SE from the number that would have been obtained if all persons had been surveyed, and about 19 chances in 20 (95%) that the difference will be less than two SEs.
3 Another measure of the likely difference is the relative standard error (RSE), which is obtained by expressing the SE as a percentage of the estimate.
4 Only estimates (numbers or percentages) with RSEs less than 25% are considered sufficiently reliable for most analytical purposes. However, estimates with larger RSEs have been included. Those estimates with an RSE greater than 25% are preceded by an asterisk (e.g. *2.2) to indicate they are subject to high SEs and should be used with caution. Estimates with RSEs greater than 50% are preceded by a double asterisk (e.g. **1.5) to indicate that they are considered too unreliable for general use.
CALCULATION OF STANDARD ERRORS
5 Standard errors can be calculated using the estimates (numbers or percentages) and the corresponding RSEs. For example, the estimated number of persons who reported to police that they were victims of physical assault in the last 12 months in New South Wales was 75,000. The RSE for this estimate is 14.8%. The SE is calculated by:
6 Therefore, there are about two chances in three that the value that would have been produced if all dwellings had been included in the survey will fall within the range 63,900 to 86,100 and about 19 chances in 20 that the value will fall within the range 52,800 to 97,200. This example is illustrated in the diagram below:
A statistical significance test for a comparison between survey estimates can be performed to determine whether it is likely that there is a difference between the corresponding population characteristics. The standard error of the difference between two corresponding estimates (x and y) can be calculated using the formula in paragraph 5. This standard error is then used to calculate the following test statistic:
If the absolute value of this test statistic is greater than 1.96 then the two estimates are said to be statistically significantly different at the 5% level: that is, there is less than 5% chance that the two estimates could have differed by as much as was observed had there been no difference in the two population characteristics. Otherwise, it cannot be stated with confidence that there is a real difference between the populations with respect to that characteristic.
For further information about the data quality of the Crime Victimisation Survey, please refer to Crime Victimisation, Australia.
DATA QUALITY: ADMINISTRATIVE DATA
The offence categories used for the 2008 reference period for Recorded Crime – Victims are based on the Australian Standard Offence Classification,
1997 (cat. No. 1234.0) (ASOC97). The offence categories used for the 2009 reference period are based on the Australian Standard Offence Classification,
2008 (second edition) (cat. No. 1234.0) (ASOC08). ASOC provides a uniform national statistical framework for classifying offences.
The introduction of ASOC08 had limited impact on the Recorded Crime – Victims data due to minimal change to the activities included or excluded for the selected offences published for the collection. The primary impact was on the offence category of other theft, with data relating to fare evasion coming into scope of the collection. Other theft was not included in the analysis in this paper and the impact on the remaining offence types was limited.
During the course of the revised classification being implemented, jurisdictions also rectified a number of local offence codes that were miscoded to ASOC in previous years, thus impacting on data comparability between 2009 and prior years for certain offences. This has primarily affected the offence categories of other theft and assault for a number of jurisdictions resulting in increased victim counts.
OUTCOMES OF INVESTIGATION
Within Recorded Crime – Victims, the stage that a police investigation has reached after a period of 30 days has elapsed since the recording of the incident by police is referred to as the outcome of investigation.
Data for the 2008 reference period includes counts for outcomes of investigations that were determined as 'no crime', where these can be identified, with the exception of Queensland. The impact of this on the analysis presented in this paper is minimal due to the small proportion of 'no crimes' for the selected offences presented for the remaining jurisdictions that included no crimes in the recorded crime data.
Data for the 2009 reference period excludes counts for outcomes of investigations that were determined as ‘no crime’, where these can be identified. The removal of this has resulted in a reduction of victim counts in comparison to 2008, in those jurisdictions where where these counts had been included. Queensland data are not impacted as these outcomes were not included in prior years. Due to systems issues, data for the Northern Territory continues to include these outcomes. The impact of excluding 'no crime' counts from the data for 2009 has led to decreases in victim counts ranging from -0.2% to -9.3%. Most changes are below 5%.
For further information about the data quality of the police recorded crime data, please refer to Recorded Crime – Victims, Australia
DATA CONFRONTATION METHODOLOGY
When undertaking any sort of comparisons between data sets, it is imperative to understand the differences between the sources such as the scope of the data, how the data is collected, counting rules applied and definitions employed. The table below outlines the key metadata for the Recorded Crime – Victims and Crime Victimisation, Australia datasets.
BROAD COMPARISONS BETWEEN DATA SOURCES
ADJUSTMENTS MADE TO ACCOUNT FOR DATA SOURCE DIFFERENCES
|Collection||Recorded Crime – Victims, Australia||Crime Victimisation, Australia|
|Collection Mode||Information on victimisation is collected by the ABS in aggregate form from administrative records held by police agencies within each state and territory. ||The Crime Victimisation Survey is conducted using the Multipurpose Household Survey vehicle (MPHS). Data is collected using Computer Assisted Interviewing (CAI) whereby responses are recorded directly onto an electronic questionnaire in a notebook computer, usually during a telephone interview.|
|Counting Unit||The counting unit for the Recorded Crime – Victims collection is "victim". A victim can be a person, an organisation, a premise/place, or a motor vehicle, depending upon the offence. Victims who were recorded by police only are included in this collection.||There are two counting units for the survey:|
1. victim - a victim can be either a person who is usually resident in a private dwelling, or a household.
2. incident – a single occurrence of a crime event. Victims can report multiple incidents, which means the total number of victims and total number of incidents will differ.
|Reference Period||Recorded Crime – Victims data is collected on a calendar year basis. Data are compiled using the date an offence is reported to police and recorded within a reference period. This corresponds to either the date the offence was reported to police by a member of the public or when it was detected by police. The report date may not necessarily be the date when the offence occurred. This is particularly the case for homicide and related offences and sexual assault offences, where in some instances the time difference between when the offence occurred and the report/detection date may be substantial. ||The survey enumeration period spans 12 months on a financial year basis, from the 1st July through to the 30th June. Respondents are asked about their experience of crime within the 12 months prior to the survey interview. |
|Scope||The scope of Recorded Crime – Victims 2008 and 2009 includes victims of offences classified to selected divisions and/or subdivisions of ASOC97 and ASOC08 respectively. |
With the exception of motor vehicle theft, statistics relate to both completed and attempted offences, that is, those where the intent is not fulfilled. Attempted motor vehicle thefts are excluded from the scope of the collection due to difficulties in distinguishing these offences from criminal damage.
The scope excludes the following:
- Conspiracy offences
- Threats to commit an offence. An exception to this exclusion is assault where there is an apprehension that the direct threat of force, injury, or violence could be enacted. Also, for offences like robbery, kidnapping / abduction and blackmail / extortion wherein an element of threat is implicit in the nature of the crime.
- Aid, abet and accessory offences
- Deprivation of liberty offences
Offences may include those that at a later point in time were determined to be unfounded, ie false or baseless. From 2009, these counts are excluded from the data.
Some victims of minor offences may not be recorded on crime recording systems by police in all states and territories.
|The Crime Victimisation Survey is a survey of all persons aged 15 years and over, with the exception of sexual assault which is asked only of persons aged over 18 years, and excludes the following:|
· members of the permanent defence force
· certain diplomatic personnel of overseas governments,
· overseas residents in Australia, and
· members of non-Australian defence forces (and dependents)
· people living in very remote parts of Australia
· people living in non-private dwellings such as hotels, university residences, students at boarding schools, patients in hospitals, residents of homes (eg retirement homes, homes for persons with disabilities, women’s shelters), and inmates of prisons.
The exclusion of people living in very remote areas is unlikely to impact on state and territory estimates, except in the Northern Territory where they account for approximately 23% of the total population.
Persons who were living in Indigenous communities in non-very remote areas are not covered for operational reasons.
|Selected offence types||Selected offences included in the Recorded Crime – Victims collection are:|
- homicide and related offences (including murder, attempted murder and manslaughter, but excluding driving causing death and conspiracy to murder)
- sexual assault
- kidnapping / abduction
- blackmail / extortion
- unlawful entry with intent (UEWI)
- motor vehicle theft
- other theft
|Selected offences included in the Crime Victimisation Survey are:|
- physical assault
- threatened assault
- sexual assault
- break in
- attempted break in
- motor vehicle theft
- other theft
- malicious property damage
|Multiple offences||The Recorded Crime – Victims collection does not enumerate unique persons or organisations. If a person is a victim of one offence, they will be counted once. If a person is a victim of multiple offences that fall within the same ANZSOC division, the victim is counted once, and the lowest ANZSOC code recorded within that division is recorded as the offence. If a person is a victim of the same offence multiple times on the same day, the victim is counted once. If a person is a victim of multiple offences that fall in different ANZSOC divisions, the victim is counted once in each of the different divisions, meaning one victim can be presented multiple times under different offence divisions.||Victims are counted once for each separate offence type they have experienced. Multiple instances of the same offence type will be counted as multiple incidents (see information under counting unit)|
For both data sources, the counting unit used for the analysis was the victim. For the Recorded Crime –
Victims data, the victim count was restricted to persons, households and motor vehicles (for motor vehicle theft). Organisation data was excluded from the analysis as organisations were not in scope for the Crime Victimisation Survey. For the Crime Victimisation Survey data, only victims who stated the incident was reported to police was included in this analysis.
Recorded Crime – Victims data is collected in reference to a calendar year while the Crime Victimisation Survey is collected on a financial year basis. As such, comparisons between the data sources have been approximated by using the calendar year reference period for the Recorded Crime –
Victims data, with the financial year data for the Crime Victimisation Survey data. This approach was used by the UK Home Office (Smith and Hoare, 2009) in comparing the British Crime Survey with police recorded crime.
The diagram below is a graphical representation of this methodology using the 2008 Recorded Crime –
Victims reference period and the 2008-09 Crime Victimisation Survey data reference period as an example.
The 2008 Recorded Crime –
Victims data refers to reports made to police, or an offence being detected by police, between January and December 2008. The 2008-09 Crime Victimisation Survey data refer to the 12 month period prior to the respondent participating in the survey. This means that the potential span of data from the survey ranges from July 2007 (the earliest offence date for respondents who were interviewed in July 2008, ie 12 months prior to interview) to June 2009 (the latest offence date for respondents who were interviewed in June 2009). The centre point to the survey recall period is June 2008, as this is a month which overlaps for all respondents. June 2008 is also the centre point of the Recorded Crime –
Victims data. As such, the 2008-09 data for the Crime Victimisation Survey data and the 2008 Recorded Crime –
Victims data are considered a suitable approximation for comparison.
Recorded Crime –
Victims data has been restricted to victims aged 15 years and over for general offence types and 18 years and over for sexual assault, to align with the scope of the Crime Victimisation Survey. For instances where the age of the victim was unknown, these records were also excluded as it could not be determined whether they should be in scope for the analysis.
Very remote areas
Recorded Crime –
Victims data was adjusted for the Northern Territory to exclude victims living in very remote areas, to align with the scope of the Crime Victimisation Survey.
Detailed information about how each offence type is defined in the data sources and any adjustments that were made for the data confrontation exercise are provided in the table below.
Note that homicide, kidnapping / abduction and blackmail / extortion are not included in the survey so were not part of the analysis in this paper. Likewise, attempted break in and malicious property damage were included in the survey but not included in the Recorded Crime – Victims collection. Other theft is included in both data sources, however due to significant definitional differences it was also excluded from analysis.
|Broad Offence Category||Recorded Crime – Victims, Australia||Crime Victimisation Survey||Adjustments made for the analysis in this paper|
|Assault||The direct (and immediate/confrontational) infliction of force, injury or violence upon a person or persons, or the direct (and immediate/confrontational) threat of force, injury or violence where there is an apprehension that the threat could be enacted.|
· Serious assault resulting in injury
· Serious assault not resulting in injury
· Common assault
(includes attempts and threats).
Can only be recorded against the person.
An incident where anyone used physical force or violence against a respondent. Physical force or violence includes being: pushed, grabbed, shoved, slapped, hit with an open hand or fist, kicked or bitten. Includes assault in a respondents line of work and excludes incidents that occurred during the course of play on a sporting field and verbal abuse.
Includes any verbal and/or physical intent or suggestion of intent which the person believed was able and likely to be carried out.
|Due to the survey design, reporting rates for non face-to-face assaults are not available. Therefore threatened assault data is unable to be included in the data confrontation. Physical assault data from the survey is used as an approximation of total assaults.|
Attempted murder from the Recorded Crime Victims data has been added to the assault figures in the analysis presented in this paper. These incidents that are recorded as attempted murder, may have been included as physical force or violence in the survey.
|Sexual Assault||Physical contact, or intent of contact, of a sexual nature directed toward another person where that person does not give consent, gives consent as a result of intimidation or deception, or consent is proscribed.|
· Aggravated sexual assault
· Non-aggravated sexual assault
(includes attempts and threats).
Can only be recorded against the person.
|Definition of sexual assault is based on the interpretation of the respondent. Only persons aged 18 years and over were asked questions about sexual assault. ||Victims of sexual assault aged under 18 years in Recorded Crime – Victims were removed to align with the scope of the survey. |
|Robbery||The unlawful taking of property, with the intent to permanently deprive the owner of the property, from the immediate possession, control, custody or care of a person or organisation, accompanied by the use, and / or threatened use, of immediate force or violence.|
· Aggravated robbery
· Non-aggravated robbery
(includes attempts and threats).
Can be recorded against a person or an organisation.
|An incident where someone stole (or tried to steal) property from a respondent by physically attacking or threatening them with force or violence. Includes incidents of physical assault and threatened assault which also involved robbery or attempted robbery.||Matched where possible, by attempting to identify and exclude organisations in Recorded Crime – Victims.|
|Unlawful entry with intent|
|The unlawful entry of a structure with the intent to commit an offence where the entry is either forced or unforced. |
Can occur against a domestic or commercial premises.
Attempted unlawful entry is not included.
|An incident where an offender broke into the respondent’s home (primary residence).|
Includes only break-in to residential premises.
Attempted and actual break-in are collected separately.
|Residential premises only are included from the Recorded Crime – Victims data, to align with the scope of the survey. |
|Motor Vehicle Theft||The taking of another person’s motor vehicle illegally and without permission with the intent of temporarily or permanently depriving the owner or possessor of the use of the motor vehicle. Excludes attempted motor vehicle theft|
· Theft of Motor Vehicle
· Illegal Use of Motor Vehicle
Private / business use cannot be determined from the Recorded Crime – Victims data.
Motor Vehicle is the counting unit.
|An incident where a motor vehicle was stolen from any member of the household. Only includes vehicles where the primary use is for private purposes (ie excludes commercial vehicles).|
Motor vehicle theft incidents are collected as household level data.
|As the differentiation between private / business vehicles is unable to be determined using Recorded Crime – Victims data, there may be more vehicles included in the Recorded Crime – Victims data in comparison to the Crime Victimisation data which excludes commercial vehicles. |
Illegal use of motor vehicle data is included for Recorded Crime – Victims as these incidents may be recorded within motor vehicle theft in the survey.