Sentencing in New Zealand: a
statistical analysis
Foreword | Acknowledgements | Executive Summary | Introduction | Chapter 2 | Chapter 3 | Chapter 4 | Chapter 5 | Chapter 6 | Chapter 7 | Chapter 8 | Chapter 9 | Chapter 10 | Chapter 11 | References | Appendix I | Appendix II | Tables | Figures
3.1 Relationships between selected explanatory variables
3.2 Trends in the explanatory variables
3.1 Relationships between selected explanatory variables
An understanding of the interrelationships between explanatory variables is required to assist with interpreting the relationships between these variables and the use of different sentences.
For example, the choice of sentence is likely to be influenced to a significant extent by the seriousness of the offence committed. Very serious offences will almost always result in imprisonment, while minor offences will more often result in a fine. Therefore, any other variable that is correlated with seriousness will also be correlated with the probability of receiving a prison sentence. The independent effect of that variable may actually be less once the effect of seriousness is taken into account. Conversely, some of the apparent effect of seriousness may be due to other factors.
Most of the variables used in this study show some relationship with the seriousness of the current major offence (Figure 3.1). The average seriousness tends to increase as the number of charges in the current case increases, at least over the range from one to about six charges. People convicted on several charges in their current case also tend to have a more extensive past criminal history (Table 3.1).
The average seriousness also increases with the weighted sum of previous seriousness scores, the rate of conviction (i.e. the frequency of offending or number of charges proved per year) and the number of previous proved cases, although the difference in the average seriousness score is not great between offenders with a few and those with many previous cases.
The average seriousness score for first offenders is anomalous in that it is higher (at 46) than the average for offenders with one previous case (35). This result is almost certainly due to the diversion of many first offenders who have committed offences of relatively low seriousness, as offenders successfully diverted through the Police Adult Diversion Scheme do not have their outcome recorded as a proved case (and therefore they do not appear in the data used for this study). Hence, first offenders who do appear in the data tend to have committed more serious offences.
Figure 3.1: Relationship between the average seriousness score (on the y-axis) and selected variables, 1995
The offence categories used in this analysis have very different average seriousness scores, the highest average being for serious offences against the person (homicide, serious assault, kidnapping, robbery and sexual offences). Traffic offenders are notable for their low values for all the criminal history variables (Table 3.1). In particular, people convicted for the less serious types of traffic offences form a very large proportion of first offenders.
If the most recent case prior to the current case resulted in one of the more serious sentences, especially imprisonment, the current case also tends to be more serious and the offender is more likely to have an extensive previous criminal history.
Table 3.1: Average values of selected variables by current offence and previous criminal history, 1995
1 Proved charges per year between the date of the first and current proved case.
2 Weighted sum of the seriousness score of the seven previous cases.
Most youth offenders (those aged less than 17) are diverted from the formal court process, leaving only the most serious offenders to be dealt with by the courts. Hence those young people who do have a proved case recorded in the data-base tend to have committed a very serious offence (Table 3.1). They also most often appear as 'first offenders' (or more accurately as offenders with no previous recorded proved case). For adult offenders the main trend is an increase in the number of previous cases through the late teens and twenties.
Females are more likely than males to be convicted for offences of low seriousness, to have fewer previous cases and to have a lower past seriousness score (Table 3.2). Māori and Pacific offenders have a higher average seriousness score for the current major offence than Pakeha/Other offenders (i.e. all non-Māori, non-Pacific ethnic groups combined). Māori offenders are also more likely to have several previous cases and a higher past seriousness score.
Table 3.2: Average values of selected variables by demographic group, 1995
1 Proved charges per year between the date of the first and current proved case.
2 Weighted sum of the seriousness score of the seven previous cases.
3.2 Trends in the explanatory variables
The recent trends in sentence use have been influenced by changes in the type of offences dealt with by the courts, as documented in a previous report (Triggs 1998). In particular, the criminal courts are dealing with more serious offences on average now than a decade ago. Between 1983 and 1995, the average seriousness of offences in this analysis increased by over 50% (Table 3.3). This is due to a combination of factors:
Table 3.3: Average values for selected variables and the percentage change in the average between 1983 and 1995
A new finding is the extent of the increase in the average number of previous court cases per offender (Table 3.3). This has almost doubled, from an average of under four previous cases per offender in 1983 to almost eight previous cases in 1995. The average past seriousness (the weighted sum of the previous seven seriousness scores) has also increased significantly, with a shorter average time since the most recent past case.
Although the average number of previous cases has increased, the overall rate of conviction (the number of proved charges per year) has changed relatively little. Thus, while the average number of proved charges per year has hardly changed, the average number of previous cases has still increased due to an increase in the average number of years over which convictions have accumulated, as discussed below, as well as a slight increase in the number of proved charges per case.
The average number of previous prison and community-based sentences has also increased between 1983 and 1995, especially for periodic detention and community service. As community service was only introduced in 1981 and has increased in use greatly since then, the marked increase in the number of previous community service sentences per person is not surprising. Community programme (formerly community care) was not introduced until 1985, so no percentage change over the 1983-95 period is shown.
These trends have been strongly influenced by the decreasing number of first offenders whose court cases result in a proved outcome. For example, just under half of the total increase in the average number of previous cases per offender is due to a reduction in the number of first offenders. The number of proved, imprisonable cases involving first offenders has decreased by 35% between 1983 and 1995. Far fewer first offenders appear in the proved case statistics in 1991 and 1995 compared to 1983 and 1987, due to the large number of first offenders who go through the Police Adult Diversion Scheme (who have their cases withdrawn) and due to the processing of most youth offenders aged under 17 through Family Group Conferences.
The first offenders who do appear in the proved case statistics by 1995 had also committed more serious offences (an average seriousness of 46) compared to 1983 (average seriousness 17), as the less serious cases are more likely to be diverted. By 1995, a number of people who appear to be 'first offenders' according to their official criminal histories may in fact have made an appearance at a Family Group Conference or have been diverted as adults.
However, even if first offenders are excluded from the analysis, there is still a significant increase in the average number and seriousness of previous cases. There were almost twice as many offenders in 1995 than in 1983 who had six to ten previous proved cases and over three times as many offenders who had more than ten previous proved cases. In contrast, the number of offenders with one previous proved case showed a small decrease and the number of offenders with two to five previous cases showed only a small increase.
The increasing number of offenders with a large number of previous cases is largely a reflection of the growing number of older offenders (especially offenders aged 30 or more) and their increasing average length of 'criminal career', with an associated increase in their number of previous convictions. Between 1983 and 1995 the number of proved, imprisonable cases involving people aged 30 or more doubled, while the number of older offenders with more than ten previous cases increased by over five times. The average number of years between the first and last recorded case (the current 'criminal career' length) increased from 7.5 years in 1983 to 14.3 years in 1995 for offenders aged 30 or over.
The number of proved cases involving people aged 25-29 has also increased significantly (by 79%), while the number of these offenders with more than ten previous cases increased by over three times. The average 'criminal career' length for 25-29 year olds increased from 6.4 years to 8.6 years over the 1983 to 1995 period.
In comparison, the number of proved cases involving people aged 20-24 showed a smaller overall increase (18%), although the number with more than ten past cases increased by 64%. The number of proved cases involving people aged 17-19 decreased slightly between 1983 and 1995 and there are seven times fewer proved court cases involving youth offenders (aged less than 17), mainly due to diversion of youth offenders from the formal court process following the introduction of the Children, Young Persons, and Their Families Act 1989.
Thus, there have been significant changes since 1983 in both the type of offences and the type of offenders dealt with by the courts. These changes would be expected to have a significant impact on the type of sentence imposed, even if sentencing practice on a case-by-case basis has not changed. In this report, each sentence is examined to quantify the extent of the changes and to assess whether sentencing practice has also changed.
