4.5  Estimating the volume of crime

Not all incidents of crime are reported to the Police. Moreover, the Police do not record all incidents that are reported to them. To arrive at an estimate of the ‘true’ level of crime, an estimate of the number of offences either not reported to, or not recorded by, the Police needs to be added to the official recorded crime statistics.[1]

This is most commonly achieved by grossing up the recorded crime figures using ‘multipliers’. Appropriate multipliers for the various categories of crime can be derived from comparing victim of crime surveys with recorded crime statistics. However, victim of crime surveys have the following limitations:

• the sample size is usually relatively small;
• participants’ recall of events may be incomplete;
• some victim categories (e.g. businesses, institutions and people aged less than 15) are typically excluded;
• surveys do not always classify crimes using the official Police categories – and in some cases do not cover particular categories of crime.

There is a conceptual problem with using multipliers in that costs are in all likelihood lower, on average, for unreported than reported crimes. Thus if unit costs (e.g. property lost) have been calculated on the basis of observed costs from reported crimes (e.g. from insurance company payouts for burglaries), there is a risk that overall costs may be overstated, possibly by a considerable amount.

To develop multipliers for New Zealand we have reviewed recent and similar studies in the UK and Australia. This is mainly because the multipliers derived from the New Zealand National Survey of Crime Victims 2001 are not readily convertible to the particular crime sub-categories covered in this study. We have generally preferred to follow the UK multipliers (except where noted in the Appendix) because they relate to the 2003/04 timeframe used in our study, whereas the Australian estimates relate to an earlier period (2000/01) and, in many cases, are themselves based on previous UK multiplier estimates. We consider that the criminal justice system and institutions in the UK are reasonably similar to those in New Zealand, although reporting and recording practices may differ.

The multipliers and derived estimates of the number of criminal acts by category as used in this study are summarised below in Table 2 (see the Appendix for details of the underlying assumptions).

These multipliers suggest that offences against private property are more likely to be reported than offences against the person. This may be because people are motivated to report property crimes to the Police for insurance purposes. People may also tend to consider some offences against their person as a private matter. Alternatively, reporting imposes costs that some victims may be unwilling to incur (such as the time taken to file a complaint, or to give evidence).

For offences with no direct or intended victim a multiplier of one is assumed, mainly in the absence of any better data. Given that the costs associated with these offences are largely those accruing to the justice sector (detection, investigation, etc.) and so are automatically captured, we consider this assumption to be not unreasonable. However, to the extent that there are also likely to be some health sector, lost output and intangible costs accruing to third parties from unreported or unrecorded offences of this type, the estimated total volumes will be understated.

Classification difficulties aside, some of the multipliers in the above table appear high relative to the findings in the New Zealand National Survey of Crime Victims 2001. We would welcome any further work to refine the above estimates in the New Zealand context.