Equality before the law, parity of sentence

Some general points on disparity of sentence can be gleaned from Green v R; Quinn v R [2011] HCA 49 (6 December 2011). The case needs to be read in its statutory context which includes a constraint on prosecution appeals against sentence. But aside from that,

• An appeal by an offender on the basis that his sentence was excessive by comparison to that imposed on a co-offender may be allowed to avoid disparity, even if the result is an inadequate sentence, as long as the result is not an affront to the administration of justice (French CJ, Crennan and Kiefel JJ at 33).
• A prosecution appeal against sentences imposed on some co-offenders should not give rise to a disparity with more lenient but un-appealed sentences imposed on other co-offenders (French CJ, Crennan and Kiefel JJ at 37).
• An appeal court should not introduce procedural unfairness by basing its judgment on a perceived defect in the decision of the court below when on the hearing of the appeal the defect was not mentioned and was not the subject of argument (French CJ, Crennan and Kiefel JJ at 76, 80).
• Intermediate courts of appeal should only overrule their own decisions infrequently and in exceptional circumstances, when the earlier decisions are manifestly wrong and not based on principle worked out in clear lines of useful authority (Heydon J dissenting in the result).
• Parity must not be conflated with proportionality, because the starting point is the appropriate sentence for the particular offence. Different offending may justify different sentences which should not be criticised as being disparate (Bell J dissenting, Heydon J agreeing, at 125).
  Prosecution appeals may not be allowed if the result would be disruption to rehabilitation, as the benefit of guidance to other courts may come at too high a cost in terms of justice to the individual (French CJ, Crennan and Kiefel JJ at 43).