59 The parity principle has been the subject of frequent consideration in this court in recent times. It is useful to draw upon what Hall J said in JOD v R [2009] NSWCCA 205:
"[60] The principle of parity requires that co-offenders receive the same sentence only if all other things are equal. Gibbs CJ In Lowe (supra) described the operation of the parity principle in the following terms at 609:-
"It is obviously desirable that persons who have been parties to the commission of the same offence should, if other things are equal, receive the same sentence , but other things are not always equal, and such matters as the age, background, previous criminal history and general character of the offender, and the part which he or she played in the commission of the offence, have to be taken into account. " (emphasis added)
[61] To similar effect were the observations of Dawson and Gaudron JJ in Postiglione (supra) at 301:-
"Discrepancy or disparity is not simply a question of the imposition of different sentences for the same offence. Rather, it is a question of due proportion between those sentences, that being a matter to be determined having regard to the different circumstances of the co-offenders in question and their different degrees of criminality."
[62] Accordingly, in general terms, the parity principle involves a question of due proportion between the sentences of co-offenders to be determined by considering the different degrees of criminality and the different circumstances of the co-offenders in question.
[63] The parity principle is only engaged where the alleged disparity is such as to give rise to a justifiable sense of grievance. As Kirby J observed in Postiglione (supra) (at 337):-
"So long as the sentencing Judge has taken into account the relevant considerations of law and fact, the appellate court will not ordinarily intervene merely because some arguable discrepancy appears between the sentencing of otherwise apparently connected or like offenders."
[64] The test for determining the existence of a sense of grievance is objective. The applicant must show that a reasonable person, looking at the circumstances of the case, would regard the offender's grievance as justified: Regina v Ilbay [2000] NSWCCA 251 Grove J (at [6]).