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Logistic regression87 _{was used to model the association between the probability of a conviction (by}

verdict, plea or proven offence) and factors such as:

 the type of offence – sexual assault and indecent assault

 the court in which the case was heard (Local Court or higher courts)

 the interval between the date of the offence and the finalisation date for that matter88

 the year the matter was finalised89 _{(using data from 2002 onwards)}

 the gender of the defendant

 the age of the defendant at finalisation.

All possible three-way interactions between the six predictor variables were tested individually in models that contained all main effects and two-way interactions.90 _{One three-way interaction was}

87 _{The logistic regression allowed the simultaneous testing of the various factors included in the model (for example,}

year of report and offence category) and assessed their effects while holding the other factors in the model constant.

88 _{When there was more than one offence, and they occurred at different dates, this was based on the date of the}

earliest offence. The categories for intervals were <1 year, 1–2 years, 2–5 years, 5–10 years, 10–20 years and >20 years.

89 _{The model was based on data from 2003 because of missing data on the date of the offence; hence the delay between}

the date of the offence and finalisation date for the higher courts before 2002.

90 _{For this analysis, the data were aggregated such that a given defendant was included for each finalisation date, for}

each offence type (sexual assault or indecent assault) for which they were charged, and also for each type of court in which they appeared. For example, a person could appear more than once in a year if they had two different finalisation dates in that year (this was rare) and/or if they had charges in more than one of the offence categories (this was much more common). The total number of observations in the aggregated dataset was 7,659, although the number used in analyses was reduced to 7,630 because of missing data. The possible effect of the lack of independence of observations

120 retained, and the model was then further reduced by removing two-way interactions that were not contained in the three-way interaction and were not significant at the nominated alpha of .001. The final reduced overall model was significant91 _{and the main and interaction effects were:}

 a significant three-way interaction between the type of offence, the court in which it was finalised and the defendant’s age at finalisation92

 a significant two-way interaction between court and the interval between the date of the offence and the finalisation date (referred to as the delay)

 year of finalisation.

The main effect of year was not involved in any significant interactions. It showed an overall increase across the period 2003–14 in the likelihood of a conviction adjusted for all other effects.93

The only main effect (other than year of report, which was not involved in an interaction) was the gender of the defendant, which was not statistically significant; the overwhelming majority of the defendants were male.

The interaction of most interest is shown in Figure 41 – the delay between the offence and finalisation by court. Figure 41 shows a significant difference in the likelihood of conviction associated with the length of the interval between the earliest offence date and the finalisation date in the Local Court, but not in the higher courts. The probability of conviction in the higher courts for the most serious offence with which a defendant was charged (mostly sexual assault) remained fairly consistent (ranging between 54 per cent and 63 per cent) over the different ‘time

for the same person, both within and between finalisation years, was taken into account during significance testing using the methodology described by Williams (2000) and implemented in Stata 13 (Statacorp, 2013).

91 _χ 2 _{(N = 7,630) = 404.4, df = 30, p <.0001.}

92 _{The odds ratio for the three-way interaction, involving the type of offence, court and age of the defendant}

(χ2 _{(N = 7,630) = 56.4, df = 1, p <.0001), resulted from the relatively low probability of a conviction for sexual assault}

charges in the Local Court for defendants who were older at the time of finalisation. While statistically significant, these are not important effects given the relatively small number of defendants facing sexual assault charges in the Local Court and the low overall conviction rate in that court for this offence; as Figure 28 shows, the numbers fluctuated between 26 in 2003 and 74 in 2008, with 68 in 2014. Defendants facing sexual assault offences in the Local Court were significantly less likely to be convicted than those facing indecent assault charges in that court (OR = 0.13), or in the higher courts (OR = 0.50). The odds of a conviction for sexual assault in the higher courts were 13.7 times those for the Local Court.

93 _{From 2008 onwards, the odds ratios comparing the conviction rates for each year with those in 2003 were all greater}

121 gaps’ between the offence and finalisation of the matter.94 _{However, in the Local Court, there is a}

marked downward trend in the probability of a conviction as the interval gets longer: from 35 per cent for the shortest gap of less than a year to a low of only 8 per cent for a gap of more than 20 years.95 _{This is despite the greater probability overall of a conviction for indecent assault,}

the more common offence in the Local Court, than for sexual assault. The probability of conviction was significantly greater in the higher courts than in the Local Court at all levels of delay.96 _{It is}

worth noting that matters heard in the higher courts were finalised with markedly longer periods between the offence and finalisation than those in the lower courts. As outlined earlier, the median interval between the date of the offence and finalisation in the Local Court was 11 months, and the mean was 38.4 months (SD = 75.4). In the higher courts, the median interval was 40 months, with a mean of 101.4 months (SD = 123.7 months). More than one in four (28 per cent) was finalised at least 10 years after the offence (see Figure 39).

Figure 41. Adjusted probability of conviction by court and interval between the offence and court finalisation in New South Wales

94 _{The odds ratios for the comparison between the shortest delay and each successive delay ranged between 0.71 and}

0.82 and, except for delays between two and five years, did not differ significantly from 1.

95 _{The odds ratios ranged from 0.13 to 0.98.}

96 _{Another way of illustrating this is with reference to the odds ratios comparing the odds of conviction in the higher}

courts versus those in Local Court over the delays: at the shortest delay, the odds ratio is 13.7; it then drops to 9.9 for a delay of 1–2 years, subsequently rising through 11.5, 17.3 and 19.4 to 83.5 for a delay of 20+ years.

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

< 1 year 1–2 years 2–5 years 5–10 years 10–20 years > 20 years

Pro bab ili ty o f con viction Local Court Higher courts

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