1 STEYTLER J: I have had the advantage of reading the judgment of EM Heenan J. I agree with it and with his Honour's conclusion that the appeal should be dismissed. There is nothing I wish to add.

2 EM HEENAN J: This is an appeal from a decision of the Compensation Magistrates Court of 3 April 2003 on questions of law, brought to this Court by leave granted on 13 May 2003 pursuant to s 84ZW of the Worker's Compensation and Rehabilitation Act (1981) ("the Act"). Summarising the grounds of appeal and the argument presented at the hearing it may be said that there are two questions of law raised and that, in substance, they are:

1. whether in calculating the weekly payments of compensation payable to the appellant in respect of his partial incapacity caused by a disability resulting from his employment with the respondent on, or about, 28 January 1998 the "weekly earnings" as prescribed as "Amount Aa" in cl 11(2) of the first schedule to the Act include payments for "overtime" as described by the enterprise agreement in circumstances where the appellant was obliged to work "overtime" as scheduled by the employer and regularly did so; and

2. that in determining whether a subsequent injury to the appellant's left ankle occurring in December 2001 was not proved to have been caused by, or substantially contributed to, the original disability the Review Officer made errors of law in determining this question of causation by taking into account alleged irrelevant considerations.

3 On or about 28 January 1998, while working as a serviceman in the course of his employment with the respondent, the appellant suffered an injury to his left ankle. Initially he received conservative medical treatment but the injury did not improve and more extensive medical investigations and treatment followed. A variety of specialist medical opinion was in evidence, in the form of reports from consultants and others, to the effect that the injury had left the appellant with a disability affecting his left ankle which prevented him from performing his pre-accident employment but left him with a capacity for other, less demanding, work and, hence, meant that he was partially disabled. In the appellant's application referring the dispute between himself and his employer for conciliation under the Act, the appellant claimed weekly

wages from 25 December 1999 and continuing on the basis of the partial incapacity caused by the disability resulting from the worker's employment with the employer.

4 Further, the appellant also claimed that he suffered an injury to his right knee in early December 2001 caused by his left ankle suddenly giving way, placing strain on his right knee, causing it to dislocate. This second injury was claimed to have been caused, or materially contributed to, by the original disability and the appellant sought statutory allowances, in the nature of payments for the medical and other therapeutic expenses, which he incurred in having the right knee injury investigated, diagnosed and treated. It is this second episode which gives rise to the second question of law raised on this appeal.

5 The terms of employment of the appellant by the respondent are contained in the Roche Kalgoorlie Fimiston Enterprise Agreement 1994 ("EBA") for a continuous shift worker. The appellant was engaged to work a continuous shift cycle of seven day shifts, seven night shifts and three days off work followed by seven day shifts, seven night shifts and four days off work. In doing this the appellant worked a minimum average of 56.4 hours per week (or 282 hours minimum per five week cycle). The EBA prescribed that the ordinary hours would average 200 over the five week cycle (cl 12.1). Under the EBA there is a schedule of various hourly rates for different classifications or grades of employee. The document provides that these hourly rate payments "are in recognition of each ordinary hour worked". Clause 14.2 provides that the employer's hourly rate for overtime would, in the case of the appellant and other continuous shift workers, be twice the hourly rates specified in cl 14.1 for each ordinary hour worked.

6 In practice this meant that for the appellant working as a continuous shift worker on the five week cycle the first 40 hours per week of each cycle were remunerated by a wage calculated at the hourly rate for "each ordinary hour worked" and that for hours worked per week in excess of 40 hours the remuneration was double the ordinary hourly rate (EBA - cl 142). Accordingly, for the minimum extra 16.4 hours per week (82 hours per five week cycle) the appellant was paid twice the ordinary time rate and, presumably, further hours worked in excess of the 56.4 hours per week also entitled him to remuneration at double the ordinary hourly rate. Importantly, the appellant was obliged to work a minimum average of 56.4 hours per week on the continuous shift roster and was not at liberty to work only 40 hours per week. His total weekly remuneration, therefore, was calculated by the application of the hourly wage rates, applied to the first 40 hours per week worked and to double those rates for the minimum extra 16.4 hours per week required to be worked and, indeed, any longer time actually worked.

7 The application of these hourly wage rates, to the aggregate time required to be worked per week, or per cycle, was effected by describing the first 40 hours as "ordinary hours worked" and for the additional hours as "overtime". The significance and effect of this distinction and, more particularly the use of the word "overtime" to apply to hours worked beyond 40 hours per week goes to the heart of the first question of law raised on this appeal.

8 As will be seen the question really is whether the description of "overtime" to the time worked after the first 40 hours per week but paid at double rates, is an apt description at all, and in particular a description which corresponds with the term "overtime" where that is used in Sch 1 cl 11 of the Act or whether the use of the term "overtime" in the EBA is simply an example of the employer designing its own dictionary by employing a word in common parlance and use in industry, but in a manner which does not correspond with the accepted sense of the term and, in particular, with the meaning of "overtime" as found in cl 11 of the First Schedule.

9 The order of the Review Officer made on 12 July 2002 required the respondent employer:

1. to pay the appellant weekly payments of compensation calculated as total incapacity payments, less the amount he could earn through entry-level wages as a fork-lift driver.

2. The parties have liberty to apply for quantification of order 1.

10 In those broad terms the order does little to reveal what in fact was determined by the Review Officer's decision. However, fortunately, this is not in dispute and an analysis of the Review Officer's reasons for decision, the Compensation Magistrate's reasons for decision and the notices of appeal, first to the Compensation Magistrate, and second to this Court, enable the substance of what was resolved by those orders to be identified.

11 In the first place the Review Officer decided that the appellant was entitled to be paid weekly payments of compensation for partial incapacity as for portions of the period since the original injury on 28 January 1998 to date and continuing. Second, the Review Officer decided that the amounts of the weekly payments were ascertainable (after the first four weeks calculated in accordance with "Amount A" prescribed by cl 11(2) of the First Schedule to the Act), by calculations made in accordance with "Amount Aa" referred to in cl 11(2) of the First Schedule less the weekly earnings payable to an entry level forklift driver. Liberty to apply was reserved for further evidence to be taken in order to calculate the precise amounts payable in accordance with this formula. Third, the Review Officer decided that the appellant had not proved that the subsequent injury to the right knee had been caused, or materially contributed to, by the original disability and, accordingly, dismissed the claim for the recovery of statutory allowances for the medical expenses and other therapeutic costs occasioned by that second injury. Although not expressly identified in the formal order of 12 July 2002, the decision of the Review Officer went further in determining the method of calculating the amounts of the weekly payments for partial incapacity to which the appellant was entitled. The Review Officer decided that, after the first four weeks of incapacity, the weekly earnings of the appellant must be calculated in accordance with "Amount Aa" in cl 11(2) of Sch I and that this meant that only the remuneration prescribed by the EBA for the first 40 hours of each week of the five week cycle could be counted. In other words the decision was that all payments which had formed part of the appellant's pre-accident weekly remuneration by the application of double the standard hourly rates for the additional 16.4 hours per week minimum or more worked could not form part of the appellant's "weekly earnings" because these were for "overtime".

12 The appeal from the Review Officer to the Compensation Magistrate, on questions of law, pursuant to s 84ZN(2) of the Act was on the following grounds: first that the Review Officer had erred in law in excluding from the calculation of weekly earnings, the double hourly rate remuneration for the 16.4 hours per week which the appellant was obliged to work in addition to the first 40 hours per week and, second, that the Review Officer had erred in law by taking into account irrelevant considerations when deciding to dismiss the claim for medical expenses and other statutory allowances in respect of the later injury to the appellant's right knee.

13 The learned Compensation Magistrate dismissed the appeal with costs by order dated 3 April 2003. In her Worship's reasons for decision it is apparent that she also concluded that the double rate of hourly remuneration for the extra 16.4 hours per week which the appellant was obliged to work after the first 40 hours, did not form part of the appellant's "weekly earnings" within "Amount Aa" in cl 11(2) of the Sch I because it was overtime.

14 Second, the learned Compensation Magistrate decided that no error of law had occurred in the Review Officer's decision to dismiss the claim made in respect of the later injury to the right knee because the Review Officer's decision was one on a question of fact alone. Her Worship concluded that this involved nothing more than the Review Officer not being satisfied, to the requisite standard of proof, that an allegation of causation made by the appellant, who bore the onus of proof on this issue, had been made out. This aspect of the case can be left for examination later in these reasons.

15 Consequently, the issues arising on this appeal require this Court to determine whether or not the regular remuneration which the appellant received before the accident, at double hourly rates, for the last 16.4 hours of his average working week formed part of his "weekly earnings" which should have been included in the calculation of the appellant's entitlements for partial incapacity or whether, as decided on both occasions, this is excluded from the computation of those payments on the grounds that it is "overtime". The second question, already identified, is whether there was an error of law by the Review Officer in making the decision to dismiss the claim for compensation arising from the later injury to the right knee.

16 The appellant's entitlement to compensation in this case arises from s 18 of the Act which obliges the respondent to pay compensation in accordance with Sch 1. In this case cl 7(2) of Sch 1 applies. It prescribes:

"7(2) Subject to section 56 and subclause (3), where partial incapacity for work results from the disability, a weekly payment during the partial incapacity equal to the amount by which the total weekly earnings of the worker calculated and varied in accordance with this Schedule would exceed the weekly amount exclusive of payments for overtime or any bonus or allowance which he is earning or is able to earn in some suitable employment or business after the occurrence of the disability."

17 The "weekly earnings" referred to in cl 7(2) have the special meaning given to that phrase by cl 11. For present purposes the appellant's entitlement is determined by cl 11(3) which provides:

"(3) In the case of a worker whose earnings are prescribed by an industrial award when the disability occurs, weekly earnings are -

(a) for the 1st to the 4th weekly payments: Amount A but not more than Amount C or less than Amount D;

(b) for weekly payments after the 4th: Amount Aa, or a lesser amount determined in accordance with the regulations, but not more than Amount C or less than Amount D."

18 This clause applies because the EBA affecting the appellant's employment comes within the extended definition of an industrial award, in s 5 of the Act. Furthermore, for present purposes, the application of cl 11(3) only involves the applications of Amount A and Amount Aa. Those terms are defined by cl 11(2) of the schedule as follows:

"'Amount A' means the rate of weekly earnings payable, at the time of the incapacity, for the appropriate classification under the relevant industrial award, or which would have been payable if the relevant industrial award were still in operation, plus -

(a) any over award or service payments paid on a regular basis as part of the worker's earnings;

(b) overtime_;_ and

(c) any bonus or allowance;

'Amount Aa' means the rate of weekly earnings payable, at the time of the incapacity, for the appropriate classification under the relevant industrial award, or which would have been payable if the relevant industrial award were still in operation, plus any over award or service payments paid on a regular basis as part of the worker's earnings;"

19 Clearly, therefore, Mr Thompson is entitled to have his payments for partial incapacity calculated in accordance with Amount A for the first four weeks following his period off work because of his disability which commenced on 25 December 1999 and, for the weekly payments after the fourth, to be calculated in accordance with Amount Aa.

20 It is only to the weekly payments of compensation for partial incapacity after the fourth that the controversy in this litigation applies. Plainly, following the language used in the Schedule, the weekly payments of compensation after the fourth, must be calculated without regard to overtime or to any bonus or allowance payable at the time of the incapacity. No question of any bonus or allowance arises in this case and, it is necessary to identify what is the "overtime" which is excluded from the calculation of weekly earnings in Amount Aa. Clause 11(2) of Sch 1 contain further definitions which are relevant namely:

"'Earnings' includes wages, salary and other remuneration;

'overtime' means any payment for the hours in excess of the number of ordinary hours which constitute a week's work."

21 The provisions of the EBA (cl 14) already examined reveal that the language chosen by the respondent employer in that document uses the term "overtime" to refer to the method of calculating remuneration for the last 16.4 hours per week of the average working week which the appellant was contracted to perform. Hence the question is whether or not remuneration so described for part of the obligatory working week comes within the statutory definition of overtime. This is an important question and one with far reaching consequences for employees, employers and their insurers.

22 The meaning of "weekly earnings" and in particular whether or not they include overtime has varied from time to time in worker's compensation legislation. This is in part due to the fact that overtime is capable of carrying two distinct but related meanings.

23 Historically overtime meant time which was worked beyond the agreed contracted hours in circumstances where there was no obligation for the employee to perform that work unless he or she agreed to do so on each occasion when it was offered, and, similarly, when there was no obligation by the employer to offer it. Because of the lack of obligation to perform such work the practice often developed of an employer offering higher rates for voluntary overtime usually because the work had to be performed at inconvenient hours and imposed additional strains of various kinds on the employee. By this means an association grew between the concept of overtime and higher than usual rates of remuneration so that a conflation developed between the idea of overtime as time in excess of the agreed working hours and time which is remunerated at premium rates.

24 Furthermore, where work had to be performed beyond conventional hours, such as in continuous shift work, night work, or work on weekends or public holidays, the practice developed of offering premium rates of remuneration for work performed beyond conventional hours. Hence, there has developed a particular usage of the term overtime as applying to work performed outside conventional hours or in excess of conventional hours regardless of whether or not there is an obligation by the employee to work those hours or whether those are the only hours worked by that employee and therefore, while unconventional, they are nevertheless that employee's regular or ordinary working hours. From this pattern of development the original distinction between ordinary working hours and voluntary overtime is often ignored and consequently there is a usage which refers to an employee's obligation to work overtime. This may mean an obligation to work for longer than conventional working hours each week or it may mean an obligation to work unusual hours such as on night shifts or at weekends or on other holidays. Usually, but not always, time spent working "overtime" in any of these senses carries with it an obligation to be paid at higher than normal hourly rates.

25 In the present case, under this EBA and on the facts as found by the Review Officer, the appellant was required to work on a varying shift schedule which meant that, on occasions, not only did he work at unconventional hours (nightshifts) but that he regularly worked for an aggregate number of hours a week (56.4) beyond the conventional weekly working period (40 hours). His remuneration, both for the times worked the dayshifts and on the nightshifts and for the hours beyond the conventional 40 hours, involved a premium (double rates) for all additional hours worked. Consequently, if the time worked beyond 40 hours and up to 56.4 hours per week can properly be described as overtime it must nevertheless be appreciated that it is compulsory or obligatory overtime which the appellant was required to work as part of his contract of employment. By contrast, however, any time worked after 56.4 hours per week, even though remunerated at the same double hourly rate, can be regarded as voluntary overtime.

26 The first example of this legislation is the English Worker's Compensation Act 1897. Under this, overtime payments were taken into consideration in calculating the average weekly earnings "on the ground that it was an understood thing that the labourer would work overtime when required so to do": Giles Belford, Smith & Co (1903) 5 WCC 136. In relation to the subsequent UK Act of 1906 it was also held that overtime payments were part of the remuneration of a workman and should be taken into consideration as a normal incident of the employment - Skailes v Blue Anchor Line [1911] KB 360; (1910) 4 BWCC 16 per Fletcher Moulton LJ at 24. The same approach was taken in New Zealand in Pidwell v Wanganui Sash and Door Co [1917] GLR 346; Old v Thos. Borthwick and Sons (Australasia) Ltd [1948] NZLR 1148 and Gyde v Boon Brothers Ltd [1940] NZLR 779.

27 In Kezich v Leighton Contractors Pty Ltd [1974] HCA 50; (1974) 131 CLR 362 it was decided that: "The amount of the ordinary wage or salary (including any over award payment) the worker would have received for the ordinary hours he would have worked, if he were not incapacitated for work as a result of the injury" as then contained in cl 2 of the schedule to the Worker's Compensation Act 1912-1973 (WA), meant that overtime payments ordinarily paid to the worker before his injury should be taken into account when calculating his weekly earnings and hence the amount of compensation payable to him during a period of incapacity. This decision reversed a decision of the Full Court which, by majority, had held that overtime should be excluded from the calculation of the pre-accident weekly earnings of the worker. The critical passage in the definition of weekly earnings then contained in the statute was "the amount of the ordinary wage or salary ... the worker would have received for the ordinary hours he would have worked ...". Of this Gibbs J said, at 365:

"The word 'ordinary' means 'regular, normal, customary, usual'. A man's 'ordinary hours' of work are the hours during which it is usual for him to work. There is nothing in the expression 'ordinary hours' that connotes payment of any particular rate, and to understand the words as meaning 'hours during which work is done for which overtime is not paid' would be to place upon them a meaning which they simply do not bear. The expression 'the ordinary hours he would have worked' in my opinion means the same as 'the hours he would ordinarily have worked' and it is of course no reason to depart from the proper meaning of the words because the same meaning could have been achieved by a different form of words; in the collocations to which I have just referred the use of the adjective instead of an adverb does not change the sense of the expression."

Mason J reached the same conclusion and said, in a separate judgment, at 369:

"In reaching this conclusion I am influenced also by the fact that cl 2 refers to the amount of the 'ordinary wage or salary' which the worker would have received, that is, the aggregate amount of wage or salary payable for a week's work. It makes no reference to ordinary rates of pay, a concept which lies at the foundation of the respondent's argument."

28 Great reliance is placed by the appellant in this case on the decision in Kezich (supra) to support his submission that "weekly earnings" means the aggregate of the remuneration received by the employee for hours ordinarily or normally worked. Although not cited by the appellant it should be noted that this proposition is also supported by the decision in Commissioner for Government Transport v Kesby [1972] HCA 64; (1972) 127 CLR 374. However, that does not take the appellant as far as he must travel in order to succeed in this appeal. Those authorities establish that, under a formula for paying compensation for incapacity which is related to "the ordinary wage or salary receivable for the ordinary hours the worker would have worked" one looks to the pattern of working hours normally or ordinarily worked by the employee before the accident and to the total remuneration which he earned for that labour regardless of whether it included overtime or not.

29 Since the decision in Kezich the legislation in this State was amended to remove "overtime" from the calculation of the employee's "weekly earnings" and, as is now apparent from the definition of weekly earnings for periods of disability succeeding the fourth week as prescribed by Amount Aa in cl 11(2) of Sch 1 of the Act, remuneration for overtime must be disregarded. That leaves for determination in this case what is meant by "overtime" in this setting and, in particular whether, as the appellant argues, it only means time worked additional to and beyond the ordinary or regular hours of employment. A variation on this submission is the contention that where the schedule of hours required to be worked under this EBA established a weekly minimum average of 56.4 hours as being regularly worked, and worked under an obligation to do so, it would only be hours worked in excess of this, and on a voluntary basis, which would constitute "overtime".

30 At this point some examination of how the term "overtime" has been treated for different purposes in previous authorities is necessary. In Tarmac Roadstone Holdings Ltd v Peacock [1973] 2 All ER 485, the English Court of Appeal was concerned with the proper calculation of a redundancy payment to be calculated on the basis of the worker's normal working hours which were to be the number of hours worked without overtime. Under the contract of employment in that case there was no obligation for the employer to employ the worker for more than 40 hours each week although he was normally and regularly required to work for 57 hours per week. It was held (by Denning MR, Stamp and James LJJ) that voluntary overtime did not count towards the calculation of normal working hours and that a term providing for the payment of overtime rates after x hours per week accordingly meant that x hours are the normal working hours, even where there is no express term to that effect. It may be acknowledged that, in the present case, Mr Thompson was obliged to work, on average, 56.4 hours per week and that it could not therefore be said that the last 16.4 hours worked each week were voluntary overtime. However, Tarmac Roadstone Holdings Ltd v Peacock does point to the non-overtime hours of work under a contract of employment as being the normal working hours even if this is, to a large extent, the product of a particular statutory provision.

31 There is a long series of cases in Australia where it is recognised that the term "overtime" includes hours worked beyond the standard working hours for the trade or industry even though an obligation to work those extended hours exists under the contract of employment, or the relevant applicable industrial award or agreement. In these instances the obligatory working hours beyond the standard hours are usually remunerated at a higher hourly or periodic rate but the fact that they are obligatory, rather than voluntary, additional hours worked beyond the standard or ordinary hours does not prevent them being referred to as "overtime". One example of this is to be found in The Chief Inspector of Factories (Vic) v Watsford [1936] HCA 31; (1936) 55 CLR 276 a case concerning the power of a State wages board established under Victorian legislation to prohibit all work on Saturdays except at overtime rates. In a decision which held that the State legislation did not empower the wages board to prohibit all work on Saturdays except at overtime rates, Dixon J, who with Starke and McTiernan JJ constituted the majority, said at 284:

"No doubt 'overtime' is now often used in a very wide and general way of extra or increased pay, but one might reasonably expect the enactment to apply the word only to higher rates for hours worked in excess of standard hours of labour or beyond or outside the daily hours of work."

which I take to be a recognition that overtime hours could be hours an employee is obliged to work and also to include those hours for which higher rates of remuneration are paid.

32 Chalmers v The Commonwealth [1946] HCA 37; (1946) 73 CLR 19 is a case concerning the entitlement to remuneration by an officer of the State public service of New South Wales who had, under wartime arrangements, been temporarily transferred to the Commonwealth public service under terms which provided that, while in the Commonwealth public service, his rate of remuneration should be no less favourable than his rate of remuneration immediately before the transfer. While in the Commonwealth public service the officer was required to work regular overtime on Saturdays whereas this had not been required of him while in the State public service. He argued, unsuccessfully, that because he worked longer hours his rate of remuneration, and hence his overall remuneration had been wrongly diminished. This argument was rejected on the basis that he was remunerated at an annual salary and this remained unchanged. All the judgments proceed on the basis that regular service which an employee is required to perform under his engagement, but beyond normal hours, is properly characterised as overtime - see per Williams J at 37.

33 Again, in Brownells Ltd v Ironmonger's Wages Board & The Drapers' Wages Board [1950] HCA 3; (1950) 81 CLR 108, a case showing the distinction between the power of a Tasmanian wages board under State legislation to prescribe hours of work, as distinct from a lack of power to prescribe the trading hours of an enterprise, the decision proceeded on the basis that "overtime" included the remuneration for additional hours of work which employees regularly performed and which they were required to perform under their terms of engagement - see per Dixon J at 129.

34 Exactly the same approach can be seen in The King v Metal Trades Employers' Association; Ex Parte Amalgamated Engineering Union, Australian Section [1951] HCA 3; (1951) 82 CLR 208, a case concerning the power of the then Commonwealth Court of Conciliation and Arbitration to insert in an award a provision prohibiting a union of employees from being involved in any ban on overtime. In upholding the power to insert such a provision in an award the Court treated overtime as including periods which must be worked by employees under the award and not as meaning merely voluntary overtime - see per Dixon J at 245.

35 The same approach to the meaning of overtime emerges from a shipping case dealing with a dispute between the ship owner under a charter party arising because the ship was unable to load its cargo in a continuous process because of a lack of stevedoring labour - The President of India v The Moor Line Ltd [1958] HCA 24; (1958) 99 CLR 185. In that case, at 192, Dixon CJ treated loading operations beyond the ordinary hours of labour, even where compulsorily performed at higher rates, as overtime. This approach is consistent with each of the cases previously cited which attributes the meaning of overtime to hours worked beyond the standard hours for the week, or after usual hours, for which a higher rate of remuneration is payable.

36 Two further cases closely bearing on the issues in this appeal but which were not cited in argument must also be examined. The first is Catlow v Accident Compensation Commission [1989] HCA 43; (1989) 167 CLR 543 which was a case dealing with the amount of worker's compensation payable in the case of disability and, in particular, the meaning of rate of pay for "normal number of hours per week" thus raising the issue of whether the extent of the actual hours worked or the number of core hours fixed by an industrial agreement was the measure of value. In that case it was decided by majority (Deane, Dawson and McHugh JJ, Brennan and Gaudron JJ dissenting) that where a standard number of ordinary working hours had been fixed for a worker's employment, his normal number of hours per week were those standard hours excluding overtime and not the number of hours usually worked. The reasons for this conclusion are set out in the judgment of McHugh J at 561-563 but, of special significance for the disposition of this appeal, are the reasons given by his Honour for distinguishing the decision in Kezich v Leighton Contractors Pty Ltd (supra) upon which, like in this present case, the worker placed great reliance. At 565-566 McHugh J said:

"It is true that both Gibbs J and Mason J also said that the worker in Kezich 'would normally work 60 hours per week'. But, as the Industrial Commission of New South Wales pointed out in John A Gilbert Pty Ltd v Irving [1962] AR at 318, 'normal' may mean 'regular or usual, or it may mean conforming to standard'. Thus, while it was accurate in Kezich to speak of the worker's usual hours as his normal hours, it does not follow that in s 95(1) [Accident Compensation Act 1985 Vic] 'normal number' means 'usual number'. Indeed, the different context and the history of the phrase 'normal number of hours per week' in s 95(1) dictate that it be interpreted as meaning the ordinary or standard number of hours worked and not the usual number of hours worked."

37 A similar issue over whether "ordinary time rate of pay as expressed by reference to a week" contained in the Worker's Compensation Act 1988 (Tas) was a rate calculated by ordinary hours fixed by the award which applied or hours which had been agreed by contract was addressed in Scott v Sun Alliance Australia Ltd [1993] HCA 46; (1993) 178 CLR 1. It was held by Mason CJ, Brennan, Dawson, Toohey and McHugh JJ that, in that Tasmanian legislation, "ordinary time rate of pay" referred to a rate fixed by an industrial award or agreement and did not cover a rate fixed by an individual employment contract and that the words "as expressed by reference to a week" refer to the ordinary hours for a week fixed by the industrial award or agreement and not to the hours agreed to be worked each week. In the joint judgment, at 178 CLR 5, is the following passage:

"The expression 'ordinary time rate of pay' is well known in the industrial relations field in Australia and New Zealand. It and similar terms have long been used in legislation [references omitted]. Unless the context otherwise requires, 'ordinary time rate of pay' means the rate of pay for the standard or ordinary hours of work in contrast to the overtime or penalty rate of pay for hours of work other than standard or ordinary hours - Catlow v Accident Compensation Commission [1989] HCA 43; (1989) 167 CLR 543 at 555-556, 560. When expressed by reference to a week, it refers to the product of multiplying that hourly rate by the standard thirty-five, thirty-eight or forty hour week as the case may be, fixed by legislation, industrial award or agreement."

38 Finally, and consistent with this long standing line of authority there is the recent decision in Australian Communication Exchange Ltd v Deputy Commissioner of Taxation [2003] HCA 55; (2003) 77 ALJR 1806 dealing with the meaning of "ordinary time earnings" in the Clerical Employees Award (Qld) which obliged an employer to contribute an amount equal to three per cent of the employee's "ordinary time earnings" to an approved superannuation fund. The employer had calculated the superannuation contributions by reference to the amount paid to workers for the work performed during ordinary working hours, as fixed by the award, but had made no contributions in respect of earnings paid for work done outside those hours or on overtime. The stance of the employer was upheld (McHugh, Gummow, Callinan and Heydon JJ, Gleeson CJ, Kirby and Hayne JJ dissenting) on the basis that the reference to ordinary time earnings in the award was a reference to earnings for hours worked other than on overtime. The majority accepted the employer's submission that the reference in the award to "ordinary time earnings" was a reference to earnings for hours worked other than overtime hours; and accordingly, "whatever a casual employee earned by way of overtime was not part of 'ordinary time earnings' and therefore did not provide any measure of the employer's liability to contribute superannuation payments for that employee in respect of those overtime payments".

39 Returning to the present case and, in particular, to cl 11(2) of sch 1 of the Act, the definition of overtime makes use of terms which, as the authorities which have been examined reveal, now have an established meaning. When the definition is Sch 1 of the Act provides that "overtime" means any payment for the hours "in excess of the number of ordinary hours which constitute a week's work" I can see no alternative to the conclusion that the ordinary hours which constitute a week's work can only mean, the standard number of hours for which the standard hourly remuneration is normally paid for employment under the industrial award or, in this case, the industrial agreement. In other words, overtime is meant to include time worked by employees, whether on a voluntary or compulsory basis for which premium hourly rates of remuneration are paid either because they are additional to the standard hours conventionally worked or because they are outside conventional hours such as occurs when employees are engaged on shiftwork or at weekends.

40 As previously noted, the EBA under which the appellant was employed makes reference to: "the employee's ordinary weekly hours" in cl 7.2; to "ordinary hours" in cl 12.1; and to "each ordinary hour worked" in cl 14.1. These references can only mean the average 200 hours worked over the five week cycle (cl 12.1) so producing an average working week of 40 hours although, obviously, the five week working cycle of an average shift worker, will not contain any such "average week". The EBA also provides that the remuneration for a continuous shift worker for all overtime hours worked shall be double the applicable ordinary hourly rate (cl 40.2(c)), meaning that a shift worker will be paid at premium rates for all the time worked in excess of ordinary hours. In sch 1 cl 11(2) of the Act the statutory definition expressly confines the term "overtime" to the hours worked in excess of the number of ordinary hours. So, in the present case both by the application of the statutory definition and by the employer's use of language the appellant's overtime means the time worked beyond the "ordinary hours" fixed by the agreement which, on average are 40 hours per week.

41 Accordingly, I consider that the Review Officer, and the Compensation Magistrate, was each correct in concluding that the calculation of the appellant's entitlement to compensation for partial incapacity under "Amount Aa" in cl 11(2) of the schedule could not include remuneration previously received for hours worked beyond 40 ordinary hours per week identified in this industrial agreement. Accordingly, the first ground of appeal must be rejected.

Grounds 2 and 3 - Alleged Error of Law In Finding that the Right Knee Dislocation was not due to the Disability

42 These grounds of appeal can be dealt with together. The appellant submits that in reaching the finding that dislocation of the right knee was not shown to have been caused by the original disability to the left ankle, the Review Officer erred in law by taking into account irrelevant considerations on the issue of causation, in several particularised respects. Alternatively, by ground 3 it is contended that, in declining to make that finding, the Review Officer failed to exercise the jurisdiction required of him by s 84AZ of the Act to resolve the dispute. The appellant's submissions go on to attribute the same errors of law to the learned Compensation Magistrate in failing to uphold the appellant's case that the dislocation of the right knee was caused, or materially contributed to, by the established disability arising from the injury to the left ankle.

43 Before the Review Officer the appellant's case, in this regard, was that he injured his right knee in early December 2001. He claimed that this occurred when he was getting up to change television channels, and, hearing a noise elsewhere in the house and turning quickly to investigate, his left ankle gave way putting additional strain on the right knee and causing it to dislocate. Since then there have been subsequent dislocations on about three occasions. There was no medical evidence confirming the nature of the original sub-luxation and the earliest evidence of medical attention was a certificate of 27 February 2002.

44 The Review Officer correctly treated the claim for the injury to the right knee as a claim for the "sequelae" to an accepted disability. He held that it should therefore be determined by deciding whether or not it was sufficiently causally related to the original disability. In deciding against this contention the Review Officer noted that the appellant was originally mistaken about the date of the first dislocation; that he had a history of problems with his knees and ankles for many years after playing football while younger; and that there had been other knee dislocations, after the first, before his right knee condition was medically examined and reported upon.

45 In evidence before the Review Officer was a report from the attending orthopaedic and knee surgeon, Mr A Robinson FRACS dated 15 March 2002, which stated that the left ankle pain (the admitted disability) was associated with, among other things:

"Giving way. In fact the left ankle gave way in December of last year [2001] and this resulted in dislocation of his right patella. He now has a problem with recurrent dislocation of the right patella. This is occurring once every 10-14 weeks. He is undergoing an arthroscopy in the near future to elucidate this problem and to assess its difficulty of severity.

...

Right knee. I noted a small effusion in the right knee. I could not determine any muscle wasting in view of the large size of the patient's thigh.

There was some external rotation of the tibia. The patient could hyperextend the right knee by 5 degrees. There was generalized laxity of the ligaments in the right knee as well as a very mobile patella.

...

DIAGNOSES:

...

2. Recurrent lateral subluxation of the right patella."

There are a number of further references to the right knee condition which need not be repeated and, in his recommendations, Mr Robinson said:

"6. I believe by the fact the patient's left ankle gave way and rolled that this resulted in an unexpected severe force to the anterior aspect of Mr. Thompson's right knee. This caused his right knee cap to dislocate."

46 There was no other medical evidence to challenge or controvert the opinion expressed by Dr Robinson about the association between the left ankle injury and the dislocation of the right patella.

47 In those circumstances there may have been an expectation that Mr Robinson's opinion would have been accepted by the Review Officer but the Review Officer was not obliged to accept that opinion if there was some other hypothesis reasonably open on this issue of fact. Mr Robinson had first seen the appellant on 12 March 2002, some three months after the first dislocation. While he was able to confirm the existence of laxity in the ligaments of the right knee and the marked mobility of the patella from clinical examination and then to make his own unaided diagnosis of the existence of recurrent lateral dislocation or subluxation of the right patella, he was dependent upon the history given by the appellant about its origin and the circumstances of its first presentation. Clearly, Mr Robinson accepted the history proffered by the appellant in this regard and there does not appear to have been any reason for him to do otherwise.

48 Normally, one would expect that the opinion of a clinical specialist about the nature and cause of an injury, within the area of his speciality would be accepted, in the absence of other expert evidence to the contrary, even when that opinion depends to a greater or lesser extent upon a history of events given by the patient. The reason for this is that a diagnostic opinion, even one including an opinion about the cause of trauma, constitutes a professional opinion drawn from the assimilation and evaluation of many factors by the specialist not all of which may be expressly identified and not all of which may have equal weight or significance in the conclusion reached. For that reason, if it is proposed to question or reject a specialist's opinion in part or in whole, that should normally only be done after the specialist has been given an opportunity to comment upon whether or not the factor or factors relied upon to qualify or reject his opinion are accepted and have been put to him for his consideration or comment. If they are put to the specialist he might acknowledge that his opinion should be qualified or changed, or he might say that, notwithstanding a difference in history or some other factor for re-consideration, he still adheres substantially to his original view.

49 The danger in omitting to follow this course is that a lay person, who does not enjoy the benefit of specialist medical training and experience to allow him or her to assess the clinical significance of alterations to facts or circumstances, then purports to conclude that those differences must, necessarily, undermine or negative the professional opinion. Generally, therefore, tribunals of fact relying on specialist evidence, whether of a medical witness or some other expert should accept the uncontradicted evidence of a specialist if there is no substantial reason to do otherwise. But there still sometimes may be factors which are so fundamental and obvious that it is plain that the specialist opinion or conclusion cannot stand. It will always be a matter for careful evaluation to decide whether such a situation exists before rejecting uncontradicted specialist opinion.

50 Nevertheless, what clearly emerges from this scrutiny is that the acceptance or rejection of medical opinion on an issue of whether a particular event has caused a particular injury in a particular case involves a question of fact. Similarly, whether an injury occurring on one occasion can be said to have been caused, or contributed to, or has been aggravated by, some pre-existing condition will similarly be a question of fact. In the absence of any error of legal principle in applying the tests needed to decide such a question of fact, the conclusion will be unexaminable on an appeal to a Compensation Magistrate, or on a further appeal to this Court. In the present case there can be no doubt that this was an issue of fact and that it does not give rise to a question of law which can be reviewed by this Court.

51 This description of the process followed in this case demonstrates that the Review Officer addressed the issue before him and so exercised his jurisdiction under s 84ZA of the Act to resolve the dispute about the cause and existence of the injury to the appellant's right knee. Consequently the third ground of appeal must fail.

52 With regard to the second ground of appeal which submits that the Review Officer erred in law by taking into account irrelevant considerations, and that this error went uncorrected by the learned Compensation Magistrate, the alleged irrelevant considerations were:

1. The appellant could not be precise as to the date the knee injury occurred;

2. The appellant had previously worn a knee brace on his left knee;

3. The appellant had previously had problems with his right ankle;

4. The appellant weighed 105 kilograms at some time in the past but now weighed 165 kilograms;

5. Dislocations to his right knee after the first dislocation occurred in non-compensable circumstances.

53 It is immediately to be noted that all these alleged irrelevant considerations are matters of fact which the Review Officer considered when reaching his conclusion that the appellant had not established that the right knee injury had been caused or aggravated by the disability arising from the injury to the left ankle. There is not, nor could there be, any suggestion that some erroneous principle relating to the admission or rejection of evidence, or to the onus of or standard of proof was wrongly taken into account or that there was a failure to attend to any relevant principle of law in reaching a conclusion of fact on this issue of causation. As already described, the issue of fact for decision, was whether or not the appellant could establish, on the balance of probabilities, that the initial dislocation, and following subsequent dislocations, of the right patella, were caused or contributed to by the injury to the left ankle. This required the appellant to prove, on the balance of probabilities, that there had been a dislocation of the right knee, and subsequent dislocations requiring medical intervention and treatment and that the condition in the right knee had been caused by the earlier disability.

54 The appellant succeeded in showing that there had been a dislocation of the right knee and that it required medical treatment but failed to establish, to the satisfaction of the Review Officer on the balance of probabilities, that this was caused or contributed to by the original disability. In view of the uncertainty of the appellant about the date of the first occurrence and the lack of any corrobative medical record of the nature or date of that injury until much later, the Review Officer did not accept that the event had occurred in the manner described by Mr Thompson to Mr Robinson FRACS or in evidence. Further, the Review Officer took account of the previous history of occasional bilateral ankle and knee problems together with the appellant's substantial weight. It is clear that the Review Officer inferred that it was more probable that the problem in dislocation of the right knee was due to this earlier history.

55 At this point it may be said that as this was simply a question of fact, then not only did the Compensation Magistrate have no power to review it under s 84ZN(2) but neither does this Court have power to review it under s 84ZW. A failure to establish a case, to the requisite degree of proof, on the facts by a party who carries the burden of proof is a familiar form of casualty which can seldom be repaired even where there is a full right of appeal on questions of fact - see Dearman v Dearman [1908] HCA 84; (1908) 7 CLR 549 per Griffith CJ at 553.

56 These were all relevant facts for consideration and evaluation by the Review Officer and are not susceptible to review on this appeal where this Court has no jurisdiction to review findings of fact. No irrelevant consideration has been shown to have been taken into account by the Review Officer and, accordingly, I conclude that the learned Compensation Magistrate was correct in rejecting that ground of appeal. It follows that I must also reject the second ground of appeal.

57 For these reasons I consider that none of the grounds of appeal raised by the appellant has been made out and that this appeal should be dismissed.

58 LE MIERE J: I agree with the reasons for judgment of EM Heenan J and have nothing to add.

• Background
• Terms of Employment
• "Weekly Earnings" - "Overtime"
• Grounds 2 and 3 - Alleged Error of Law In Finding that the Right Knee Dislocation was not due to the Disability