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APPENDIX A
Appendix A: Defining ‘serious’ indecent assault of a
female aged 16 or over
‘Serious sexual assault of an adult female’ (SSA) has been defined in this study as
being (completed) rape of a female aged 16 or over, and serious indecent assault of a
female aged 16 or more. However, the OI classification of indecent assault of a
female, while distinguishing those victims aged under 16 from those aged 16 or
more, does not discriminate in terms of the severity of the offence. In order to
enable such a separation to be made, therefore, the length of sentence given for
convictions of indecent assault of a female aged 16 or over in 1995-7 was examined.
This offence has OI code 20, sub-code 2, and is referred to here as ‘IAF 16+’. For
this offence, offenders can be given non-custodial disposals, or a custodial sentence
of up to ten years (in addition to Hospital Orders and Restriction Orders). The aim
of this exercise was to establish what classes as a ‘severe’ custodial sentence, with a
view to using this as a measure of ‘serious’ IAF 16+. It seemed more appropriate to
consider the median, rather than the mean, sentence length, as the point at which
to separate out ‘serious’ from ‘non-serious’ offences. Furthermore, it would be
reasonable to expect the length of sentence to depend additionally on such factors
as the offender’s age and previous criminal history. These factors have been
considered in the modelling.
Using the computer package GLIM, the log of the sentence length can be modelled,
with the median then being obtained using the result:
if
then
log y N(ß’x, 2
)
median(y) = exp(ß’x)
(Aitkin, Anderson, Francis and Hinde (1989), p.121).
Previous criminal history can be considered in several ways. Those considered here
were in terms of: number of previous offences; number of previous sentencing
occasions; counting all offences; all sex offences; or only rape and indecent assault of
a female (where the victims were of any age). The model finally chosen involved
the number of previous sex offences (a four-category variable), age of the offender at
conviction (a continuous variable), and an interaction between the two, with all
these terms being statistically significant in the model.
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