The relevant legal principles
64 In considering the legal principles that are applicable to the assessment of the claim for damages in issue, the starting point is Graham v Baker (1961) 106 CLR 340. Dixon CJ, Kitto and Taylor JJ said in that case (at 347):
"[A]n injured plaintiff recovers not merely because his earning capacity has been diminished but because the diminution of his earning capacity is or may be productive of financial loss. And if, notwithstanding such impairment, both his contract of employment and his right to ordinary wages continue, how can it be said that his impairment has resulted in any loss so far as his earning capacity is concerned?"
65 The words of McHugh J in Medlin v The State Government Insurance Commission (1995) 182 CLR 1 (at 16) must be borne in mind:
"In Australia, a plaintiff is compensated for loss of earning capacity, not loss of earnings. In practice, there is usually little difference in result irrespective of whether the damages are assessed by reference to loss of earning capacity or by reference to loss of earnings. That is because 'an injured plaintiff recovers not merely because his earning capacity has been diminished but because the diminution of his earning capacity is or may be productive of financial loss'. Nevertheless, there is a difference between the two approaches, and the loss of earning capacity principle more accurately compensates a plaintiff for the effect of an accident on the plaintiff's ability to earn income. Earning capacity is an intangible asset. Its value depends on what it is capable of producing. Earnings are evidence of the value of earning capacity but they are not synonymous with its value. When loss of earnings rather than loss of capacity to earn is the criterion, the natural tendency is to compare the plaintiff's pre-accident and post-accident earnings. This sometimes means that no attention is paid to that part of the plaintiff's capacity to earn that was not exploited before the accident. Further, there is a tendency to assume that if pre-accident and post-accident incomes are comparable, no loss has occurred."
66 Mr McCracken's submissions, to a large extent, ignore that part of his capacity to earn that he did not fully exploit before the injury.
67 In Husher v Husher (1999) 197 CLR 138, Gleeson CJ, Gummow, Kirby and Hayne JJ said (at 147, [18]):
"The financial loss occasioned by impairment of earning capacity is the loss of what (if there had been no accident) the injured plaintiff would (as opposed to could) have expected to have had under his or her control and at his or her disposal by exercising that capacity. We refer to 'control' and 'disposal' because what the plaintiff has lost are the financial rewards from work that are rewards the plaintiff would have been able to direct to whatever purpose or destination he or she chose."
68 These remarks are particularly apposite in the present case. They demonstrate that, as regards his past loss of economic capacity, the issue is whether, in the relevant period, Mr McCracken incurred a loss (in comparison with what he would have earned had he not been injured) after exercising whatever earning capacity he then had. This involves examining the financial rewards Mr McCracken derived from work that he in fact had under his control or at his disposal. As Professor Luntz in Assessment of Damages for Personal Injury and Death, (Sydney: LexisNexis Butterworths, 4th ed, 2002) at [5.2.6] remarks:
"Where the plaintiff is only partially disabled, the damages to the date of trial are the difference between what would have been earned if the plaintiff had not been injured and what the plaintiff has now earned, or was capable of earning, less tax, in each instance."
69 In State of New South Wales v Moss (2000) 54 NSWLR 536, Heydon JA referred to the "two uncontroversial themes" running through the cases relating to the assessment of damages for injury to earning capacity referred to by his Honour at 551 to 552, [67] to [69]:
"Thus, in relation to the first of these themes, in Paff v Speed (1961) 105 CLR 549 at 559, Fullagar J said that the 'usual method of proving damages under [this] head is by calling evidence to show what the plaintiff could probably have earned during the rest of his life if he had not been injured and what, if anything, he is now capable of earning'. The same is true where the defendant is seeking to demonstrate that the diminution of earning capacity is only partial. Barwick CJ, in Arthur Robinson (Grafton) Pty Ltd v Carter (1968) 122 CLR 649 at 657, said of a plaintiff who had been rendered almost a quadriplegic:
'He has lost his earning capacity, so far as the evidence goes, all earning capacity. In this connexion, however, too little attention it seems to me is paid to the possibilities which have and will yet open up for paraplegics and quadriplegics: but this ought to be the subject of the evidence and not of mere suggestion on the part of judge or advocate.'
The first theme was stated with the qualification 'in general', because there is authority that in some circumstances over-elaborate evidence is unhelpful. In J K Kealley v Jones [1979] 1 NSWLR 723 at 734-735, Moffitt P said:
'Sometimes, particularly in a jury trial, evidence of some claimed prospective earnings but for injury may distract rather than aid quantification of loss. A jury may well make a better assessment of the loss of a young law student debarred by injury from becoming a barrister by evidence such as in Gilles' case [(1975) 49 ALJR 349] uncluttered by evidence of earnings made by selected leading senior counsel, with or without the aid of statistics as to success and failure rates of students and barristers, where such evidence is led in supposed aid of quantifying the lost opportunity of becoming leading counsel in the foggy future.'
This approach may rest on a general recognition that 'the task of assessing damages in personal injuries cases should be kept as simple as possible': Jongen v CSR Ltd (1992) Aust Torts Reports 81-192 at 61,713 per Anderson J.
The second theme in the authorities was summed up by Reynolds JA in Yammine v Kalway [1979] 2 NSWLR 151 at 155, as follows:
'in seeking to quantify his damages, a plaintiff could be well advised to offer [evidence of wage levels] in many cases; and likewise a defendant, in seeking to cut down the damage, might similarly be well advised to tender such evidence; neither, in the absence of such evidence, could complain, to the same effect, at any quantification arrived at. This, however, is far from asserting that in the absence of such evidence only nominal damages is appropriate. …[W]here a plaintiff has suffered a significantly disabling injury which obviously affects the range and nature of the work he can, therefore, perform, a tribunal of fact can, without specific evidence as to what other persons with that kind of disability can earn, make a judgment and assessment, on a percentage basis or otherwise, of the value of the lost capacity.'
Where the plaintiff calls incomplete evidence and there is only a low award for diminution of earning capacity, it is difficult for the plaintiff to complain: Minchin v Public Curator of Queensland [1965] ALR 91 at 93; Giorginis v Kastrati (1998) 49 SASR 371 at 375."
70 As Fullagar J observed in Paff v Speed (1961) 105 CLR 549 (at 559), the usual method of proving damages for loss of earning capacity is by calling evidence to show what the plaintiff could probably have earned had he not been injured and what he is now capable of earning, the point being that it is for the plaintiff to show what, if anything, he remained capable of earning.
71 Sugerman JA explained this in detail in Adams v Ascot Iron Foundry Pty Limited (1968) 72 SR (NSW) 120 (at 132 to 133):
"In many, if not most, cases of damages for personal injuries, damages are awarded in respect of a lost or diminished earning capacity of the plaintiff. In such cases loss of earnings in the past and prospective loss of earnings in the future furnish a guide to the measure of such damages. A plaintiff is frequently said by medical evidence to be unfit as a result of his injury for his former employment, but to be capable of doing other forms of work, eg light work with or without particular qualifications. If in such cases a question arises of the plaintiff's ability to find such other forms of work the problem is not one of mitigation of damages. It is really the plaintiff who is seeking to increase damages by establishing that he has been unable to obtain and in the future may not be able to obtain, or may only be able to obtain intermittently, work of the only kind of which he is capable. In this respect the onus of proof in the sense of the onus of satisfying the jury rests upon the plaintiff as part of the general burden which lies upon him of proving the extent of the damage he has suffered by reason of the injury.
In some cases it is the defendant who seeks to introduce evidence by way of establishing that a particular employment, usually with the defendant himself as the previous employer, within the capacity of the plaintiff is available to him. The present is an example of such a case. In such cases the defendant is really denying, according to the circumstances, that the plaintiff's incapacity is as extensive as he claims or that his loss of earning capacity is aggravated by the impossibility of him obtaining employment within the limited capacity remaining to him."
72 In Medlin v State Government Insurance Commission, McHugh J (at 21) said: