Time trend in the use of imprisonment

Figure 1: Average daily numbers in prison 1985 to 1999

50. Figure 1 above illustrates trends in the annual average daily number of people in prison (sentenced and remanded) in the 15 years from 1985 to 1999. According to the Figure there has been a reasonably constant rate of growth throughout that period, of around 275 new prison places per year, which was interrupted for three years by the effects of the 1993 Criminal Justice Amendment Act, which reduced demand for prison space by reducing sentence lengths. The effect of that steady growth has been to increase the annual average muster by 99 percent from 2,820 at the beginning of the review period, to 5,665 in 1999. During the last two years the rate of growth may have declined and current projections of prison populations to the end of 2,010 allow for an annual growth of 137 new prison places per year.⁷

51. Assuming that the lower rate of growth continues, the reduction in prison use needed to bring growth in imprisonments to zero amounts to 137 fewer prison places in the first year than current forecasts call for, 274 fewer prison places in the second, 411 fewer in the third year and so on. If Government wished to bring about a continuing modest decline in imprisonment, as measured by average daily musters - of, say two-and-a-half percent per year, then the reduced number of imprisonments in the first year would have to be 138 more than the reduction needed to bring about zero growth - a total reduction of 275 fewer prison places. To sustain the downward trend a further reduction of 275 places would be required in the second year - 550 below the current trend line, and so on.

Figure 2: Numbers of people sentenced to imprisonment by offence type 1985 to 1999

Source: Data supplied by the Ministry of Justice

52. This report recommends 275 fewer prison spaces on a compounding basis as a target for the 'reducing imprisonment' exercise. If the current lower rate of growth continues this target will achieve a modest reducing trend. If the previous high rate of growth re-emerges this target will still produce zero growth in inmate numbers in the future.

53. Figures 2 and 3 show that the steady growth in the number of inmates in the period since 1985 has been brought about by two factors - increasing numbers of people are being sentenced to prison (Figure 2), and sentences are getting longer (Figure 3).

54. In Figure 2 the number of people imprisoned each year since 1985 is disaggregated by major offence type. The graph suggests that the 38 percent increase in imprisoned offenders across the review period was brought about by a 45 percent increase in space occupied by offenders sentenced for violence. Prison sentences for property offences decreased by 27 percent, and traffic offences decreased by 2 percent. Imprisonments for traffic offences have been increasing during the last four years - up from 18.7 percent of imprisonments in 1985 to 22.4 percent in 1999.

Figure 3: Trend in avenge sentence length 1985 to 1999

Source: Data supplied bv the Ministry of Justice

55. In 1999, 28.4 percent of offenders sentenced to prison were convicted of a property offence, 27.5 percent were convicted of a violent offence, and 22.4 percent were convicted of traffic offences.

56. Figure 3 illustrates the trend in the average sentence length imposed, in the period 1985 to 1999. As the Figure shows the average sentence length has increased significantly - by more than 75 percent- across the review period. This trend to increasing sentence lengths is consistent with the increase in the proportion of imprisonments for violence, and the decrease in the proportion of imprisonments for property offences illustrated in Figure 2. While sentence lengths are increasing, this is probably due to changes in the seriousness of offences, rather than increasing sentence lengths for comparable offences.

57. Figure 4 illustrates trends in the proportion of convictions that result in prison sentences. A linear regression line fitted to the data shows almost no slope, indicating that there has been no overall change in the trend of the use of imprisonment as a sanction across the review period, and suggesting that courts have become neither more nor less likely to use imprisonment as a sanction. However, the percentage of convictions resulting in imprisonment varies from year-to-year across a 1.5 percent range.