Periodic detention
6.1 Background
Periodic detention was introduced in 1962, originally as a residential sentence for 15-20 year old offenders. In 1966, periodic detention was extended to become a non-residential sentence for any offender aged 15 or over convicted of an imprisonable offence. Periodic detention may also be imposed for non-payment of a fine, although such cases are not included in the data used for this study. As this sentence involves attendance at a work centre to undertake supervised work, the sentence can only be imposed if there is a periodic detention centre within a reasonable distance of the offender's home.
This chapter examines which statistical factors most influence the use of periodic detention sentences, looking first at the variables individually and then at their combined effects using multivariate modelling techniques. Changes in the use of periodic detention are analysed in the final section of this chapter.
6.2 Single variable analysis of current factors influencing sentencing
Overall, 24% of the offenders who had a proved case in 1995 received a periodic detention sentence.
The relationship between the seriousness of offending and the use of periodic detention is not as sharply defined as it is for imprisonment (Figure 6.1). The proportion of offenders sentenced to periodic detention is highest for offences of low to moderate seriousness (20-180 on the seriousness scale). Around a third of cases involving offences in this seriousness range result in a periodic detention sentence. This seriousness group includes offences such as aggravated assault, domestic assault, burglary, vehicle conversion, fraud and driving while disqualified. The probability of periodic detention is still significant for offences of moderate to high seriousness (180-365).
Offences of low seriousness (20 or lower; e.g. common assault, cannabis use, disorder, theft, and drink driving), as well as very high seriousness offences (more than 365; e.g. aggravated robbery, grievous assault, sexual violation) are much less likely to result in periodic detention than moderately serious offences.
Similarly, the use of periodic detention peaks for offenders with a few charges in the current case, but is not much lower for higher numbers of charges.
Figure 6.1: Percentage of offenders receiving a periodic detention sentence in 1995 for selected variables
The criminal history variables also show a significant relationship with the use of periodic detention. Offenders with several or many previous cases have a higher probability of a periodic detention sentence than those with no or a few previous cases. Offenders with moderate to high rates of conviction (5-10 proved charges per year) and a moderate to high cumulative past seriousness, and offenders who have been convicted within the past year also have a relatively high probability of receiving a periodic detention sentence.
The percentage of offenders receiving a periodic detention sentence is higher if the most recent sentence prior to the current case is also periodic detention (46%), than if the most recent sentence was a prison sentence (26%), community programme (24%), supervision (26%), community service (27%) or a monetary penalty (16%).
As for imprisonment, women are less likely than men to be sentenced to periodic detention; 15% of proved cases involving an imprisonable offence result in periodic detention for females compared to 25% for men. By ethnicity, 30% of Māori, 27% of Pacific peoples and 22% of Pakeha/Other offenders receive a periodic detention sentence. A smaller proportion of young offenders receive periodic detention than offenders in their 20s and early 30s (2% of under 17 year olds who have a proved case,4 23% of 17-19 year olds, 27% of people aged 20-29 and 21% of people aged 30 or over).
By offence type, 51% of breaches of periodic detention result in periodic detention, while all other offence types fall in the range 21-27%, except disorder offences at 14% of proved cases.
6.3 Multivariate analysis of current factors influencing sentencing
6.3.1 The fit and accuracy of the 1995 model
The logistic regression models for periodic detention achieved a significant overall fit to both the full and half 1995 data, as indicated by log likelihood ratios significant at the 0.0001 level of probability and a non-significant residual (unexplained variation) term. The model not only fits the data it was developed on, but fits equally well to other data. Thus, the results of the test phase (Figure 6.2) show that the model developed using one half of the 1995 data (the 'fitted data') fits equally well to the other, unseen half of the 1995 data (the 'test data').
The periodic detention model differs from the prison model in that the results are only close to the ideal line up to a probability of about 0.6. Beyond a probability of 0.6 the predicted probabilities are lower than the actual probability. There were relatively few offenders whose probability of receiving a periodic detention sentence was greater than 0.7. Thus, there were no factors or combination of statistical factors that adequately predicted a very high probability of receiving a periodic detention sentence. This is perhaps not surprising, given that community-based sentences are targeted at an intermediate group of offenders (those who have neither a high probability of imprisonment nor a high probability of receiving a fine or no sentence).
Figure 6.2: Plot of the predicted probability versus the actual proportion of offenders receiving periodic detention, 1995 fitted and test data
6.3.2 Results of the 1995 model
The results of the 1995 logistic model for periodic detention indicate that the most significant factors increasing the statistical probability of receiving a periodic detention sentence are (Table 6.1):
- An offence with a moderate seriousness score (seriousness scores in the range >20-180) and also offences of low to moderate seriousness (>1-20) or moderate to high seriousness (>180-365)
- a moderate number of current charges (2-4 charges)
- a current offence of breaching a periodic detention sentence
- at least one previous sentence of periodic detention
- a previous criminal history.
Table 6.1: Logistic regression model of the probability of periodic detention, 1995
Note: An odds ratio of >1.0 indicates a high relative risk (i.e. more likely to receive this sentence than the reference group). The most significant variable (highest Wald Chi-square, lowest probability P), is rank '1'.
Thus, if the most recent previous sentence served or any other previous sentence was periodic detention, especially if the recent sentence resulted in a breach of the sentence conditions, then the probability of a further periodic detention sentence is increased. There is also an increased probability of receiving periodic detention if the most recent previous sentence was community service.
In contrast, offenders who have previously served a prison or community programme sentence are less likely to receive a periodic detention sentence, as are those whose current offence is a disorder offence, a drugs offence, domestic violence, or an offence against the person (i.e. a violent offence). A guilty plea also appears to reduce the probability of receiving a periodic detention sentence.
Gender, age and ethnicity are all significant variables in the periodic detention model. Women are much less likely than men to receive a periodic detention sentence, even after differences in offence type and criminal history are taken into account. To some extent this may reflect practical issues of the available periodic detention facilities and the type of work undertaken. Also, it is not known to what extent the particular circumstances of the average case involving a woman may differ from the average for men, even when the statistically measurable variables are equal.
Youth offenders (aged under 17) have an extremely low relative risk of receiving periodic detention. This is not surprising, considering offenders aged under 15 cannot receive periodic detention and given the availability of youth supervision and community work orders as alternative sentences.
Both Māori and Pacific peoples are more likely to receive a periodic detention sentence than Pakeha/Other offenders. As for the gender difference, it is not possible to determine why this should be so without examining the particular circumstances of the average case for different ethnic groups (i.e. differences not captured by the statistical variables measured in this analysis).
Moderate levels of previous offending also significantly increase the probability of a periodic detention sentence. Rates of conviction of more than 2 charges per year, a weighted sum of previous seriousness of more than 10 (especially >10-60), not more than 4 years gap since the last conviction, and more than four previous cases are all significant predictors of a periodic detention sentence.
6.4 Changes in the use of periodic detention
In contrast to the relatively small changes in the actual percentage of proven cases resulting in imprisonment, there have been very substantial changes in the use of periodic detention between 1982 and 1997 (Figure 6.3). In 1982, 11% of all proved cases for imprisonable offences resulted in a periodic detention sentence, compared to 24% in 1997. The use of periodic detention peaked in 1991 at 28%. The total number of offenders receiving a periodic detention sentence has increased by 180% between 1982 and 1997.
Figure 6.3: The percentage of proved cases resulting in a periodic detention sentence for imprisonable offences, 1982-1997
A change in the use of a particular sentence may be due to one or both of the following: (i) a change in the type of offence or offender being dealt with by the courts or (ii) a change in sentencing practice (such that offenders with the same characteristics are now more or less likely to receive a particular sentence than in the past).
Significant changes in the use of different sentences would be expected over the 1983-95 period, given the changes in the type and seriousness of offence and the type of offender, as measured by the statistical variables used in this study (section 3.2). Specifically, the significant increases in the average seriousness of offences and the number of persistent offenders dealt with by the courts would be expected to result in an increase in the use of serious sentences such as imprisonment and periodic detention.
The aim of this research is to determine the extent of change expected from these statistical trends and then to examine whether there has been any additional change in sentence use that could be explained by changes in sentencing practice.
To test whether sentencing practice has changed with respect to periodic detention, the logistic model developed using 1995 data was used to predict the probability of receiving a periodic detention sentence for offenders in earlier years. This means that an offender in 1983 who has the same criminal history and current case characteristics as a person in 1995 would have the same predicted probability of periodic detention. The predicted probabilities are then compared to the actual proportion of people receiving a periodic detention sentence in each year. If no change in sentencing practice has occurred, then the predicted probability should be the same as the actual proportion receiving periodic detention.
The results indicate that there has been a change in sentencing practice, but also that much of the increase in the use of periodic detention can be explained by changes in statistical factors. Overall, 12.8% of offenders in 1983 received periodic detention, compared to 16.2% in 1987, 26.6% in 1991 and 23.8% in 1995 (Table 6.2). Had there been no change in sentencing practice with respect to statistical factors, the predicted probability of periodic detention would still have been lower in 1983 (17.8%) than in 1995 (23.8%), due to statistical factors such as the lower average seriousness of cases proved in 1983 and the lower percentage of persistent offenders.
The estimated increase in the use of periodic detention due to changes in sentencing practice is the difference between the actual percentage in 1983 (12.8%) and the predicted percentage (17.8%). In other words, approximately half of the overall change is due to changes in the type of offences and offenders coming before the courts, with the other half or so apparently due to changes in sentencing practice.
Changes in sentencing practice over the range of probabilities are shown in Figure 6.4. At the point of peak use, 1991, an offender was more likely to get periodic detention than a person with the same statistical characteristics in 1995 (i.e. the data points in the 1991 line all lie considerably above the 1995 line). Conversely, a statistically equivalent offender would have been less likely to get periodic detention in 1987 and 1983.
Figure 6.4: Comparison among years of the actual and predicted probabilities of periodic detention, with predictions made using the 1995 model
An indication of the extent to which different factors have influenced the changes in sentence practice between 1983 and 1995 is given in Table 6.2 and Figure 6.5. The comparison between the actual and predicted percentages for each year indicates the extent of changes in sentencing practice, once the effects of changes in statistical factors have been accounted for.
The greater actual use of periodic detention in the 1990s compared to the 1980s is most notable for offences of low to moderate seriousness (Table 6.2 and Figure 6.5.). At the lower end of the seriousness scale (>1-20) the actual probability of receiving a periodic detention sentence has increased from 9% in 1983 to 25% in 1995. At a moderate seriousness (>20-180) the increase has been from 25% to 36%.
However, much of this change, especially for offences of moderate seriousness, appears to be due to changes in other characteristics of offenders, as the predicted percentage for 1983 is not much higher than the actual percentage. Thus, offenders in 1983 had other characteristics that would be expected to lead to a lower use of periodic detention. For example, offenders convicted of offences in the 20 to 180 seriousness range in 1983 had just half the average number of previous cases of offenders in 1995 (5.3 compared to 9.7).
In contrast, the far greater usage of periodic detention for persistent offenders in the 1990s compared to the 1980s cannot be explained by changes in other characteristics, but rather appears to be a real change in sentencing practice (Figure 6.5-2a,b). At the same time, the use of imprisonment for persistent offenders has decreased (section 4.4). Therefore, the increases in the use of periodic detention are likely to have resulted, at least in part, from the decreased use of imprisonment following policy changes promoting the use of alternatives to prison.
The probability of receiving a periodic detention sentence was higher in 1995 than in 1983 for all offences, but the increase was greatest for breaches of periodic detention and other offences against justice, and for drug offences, less serious violent offences and disorder offences. These were also the offence groups that appear to have been most subject to a change in sentencing practice as opposed to a change in the statistical characteristics of the average offender. The increase in periodic detention for these offences has been paralleled by a decrease in the use of imprisonment.
In addition to the increase for breaches of a periodic detention sentence, offenders were also more likely to receive a periodic detention sentence in 1995 compared to 1983 if their most recent previous sentence was periodic detention, community service or imprisonment. These factors introduce an element of circularity into the distinction between changes due to the type of offender/offence and changes due to sentencing practice.
This circularity arises because the probability of a periodic detention sentence is increased if the current offence is a breach of a periodic detention sentence, or if the most recent or other previous sentences were periodic detention or community service. Therefore, any increase in the use of periodic detention or community service will lead to a further increase in periodic detention due to the greater number of offenders who have either breached or served these sentences. The 1995 model counts previous sentence history as a statistical characteristic of the offender to be used in calculating 'predicted probability' rather than as an outcome of changes in sentencing practice. Therefore the overall effect of changes in sentencing practice may be underestimated. The implications of these findings are discussed further in section 11.4.1.
Table 6.2: Actual percentage receiving periodic detention for each variable and year and predicted percentage based on 1995 sentencing practice
Note: The predicted percentage is the percentage of offenders who would have received the sentence had the sentencing practices of 1995 been applied, as predicted by the 1995 logistic model. The difference between the predicted percentage for 1995 and other years indicates the proportion of the total change due to changes in statistical factors (e.g. the increase in average seriousness) while the difference between the actual and predicted percentage for each year indicates the proportion of total change due to changes in sentencing practice.
Periodic detention is used much less frequently for women than men, although women showed a greater relative increase in periodic detention over the 1983 to 1995 period. Youth offenders (aged under 17) are the only group for whom the use of periodic detention has actually decreased since 1983 (Table 6.2).
Figure 6.5: Actual percentage receiving periodic detention and predicted percentage based on 1995 sentencing practice, by offence seriousness and previous conviction history, 1983-1995
Footnotes
4. Offenders aged under 15 are cannot be sentenced to periodic detention.
