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APPENDIX C
In total, therefore, 13 variables contributed to the risk score for murder. Eight of the
summary measures produced an increased risk (shown by a positive estimate in
column 2 and a relative risk contribution above one in column 4); five summary
measures lowered the risk (shown by a negative estimate in column 2 and a relative
risk contribution below one in column 4). Some of the unusual offences identified
in Table 6 are not present in the risk score. Kidnapping and blackmail are both
missing from the final score, as such activity does not further significantly change
the risk of murder once the chosen thirteen variables have been allowed for.
However, manslaughter increases the risk of murder by a factor of over eleven times,
even after controlling for the two offence codes of violence. Similarly, attempting to
pervert the course of justice (offence code 79) significantly reduced the risk of
murder by over seven times, even after controlling for other variables.
Interpretation
The estimates in the above table can be used to build a relative risk for subsequent
murder for any offender with a prior conviction. In order to consider what such a
score is relative to, it is necessary to define a typical ‘baseline’ offender with none of
the criminal career characteristics appearing in the above table. Such an offender is
allowed to have one or more prior convictions for any offences not appearing in
Table 17 (the ‘murder-neutral’ offences) which have not led to a custodial sentence
on the last sentencing occasion, but should have no convictions for any of the
offences which do appear in the above table. These ‘murder-neutral’ offences would
include, for example, burglary in a dwelling, shoplifting and car crime. We can
imagine this baseline offender to be a typical petty offender, with a string of
relatively minor offences that have not led to a custodial sentence.
Compared with this typical petty offender, it is possible to calculate a relative risk of
murder for any other offender. If any of the risk factors above appear in the criminal
history of the offender, then we multiply the relative risks together. If none of the risk
factors appear, then the relative risk would be 1.0. One example is considered below:
Example A. A 25-year-old active offender with prior offences for arson, actual
bodily harm and indecent assault of a female. This last offence leading to a
custodial sentence of six months.
The offence of arson has a relative risk contribution of 1.987; the offence of actual
bodily harm belongs in offence category 8 – other wounding etc. – which has a
relative risk contribution of 1.329. The offence of indecent assault of a female is
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