1. Each of Johnson and Ozcan refer to and apply State Government Insurance Commission v Oakley[6] (Oakley). In Oakley, Malcolm CJ in the Supreme Court of Western Australia set out three categories in which the determination of the issue of causation requires consideration of the effect of a subsequent injury. The principles were applied in a workers compensation context in Johnson where Simpson AJA said:[7]

"... the appellant invoked, and placed heavy reliance on, the decision of Malcolm CJ in State Government Insurance Commission v Oakley (1990) 10 MVR 570; [1990] Aust Torts Reports 81-003. In that case, the Chief Justice identified three categories where the issue of causation involves consideration of the effect or impact of a subsequent injury on the determination of the cause of an earlier injury (or, perhaps more accurately, the assessment of damages consequential upon an earlier injury). The observations were made in the context of proceedings at common law in which negligence is alleged, but are equally applicable to the assessment of the degree of permanent impairment resulting from injury under no-fault legislation such as the WC Act. His Honour identified the three categories as:

'(1) where the further injury results from a subsequent accident, which would not have occurred had the plaintiff not been in the physical condition caused by the defendant's negligence, the added damage should be treated as caused by that negligence;

(2) where the further injury results from a subsequent accident, which would have occurred had the plaintiff been in normal health, but the damage sustained is greater because of aggravation of the earlier injury, the additional damage resulting from the aggravated injury should be treated as caused by the defendant's negligence; and

(3) where the further injury results from a subsequent accident which would have occurred had the plaintiff been in normal health and the damage sustained includes no element of aggravation of the earlier injury, the subsequent accident and further injury should be regarded as causally independent of the first.'"

1. The principles were applied in Ozcan where the Court of Appeal accepted that impairments could be aggregated where an earlier injury made a material contribution to a later injury. In those circumstances, s 322(3) of the 1998 Act required the injuries to be assessed together because all the impairments arose from the first injury.
2. The order made by the Member in this case reflects causation under the third category in Oakley. The Member said that this was the position adopted by Mr Singh at the hearing. Mr Singh's submissions on this appeal suggest that he believed that the Member found that the injury was a disease injury aggravated in the employ of TAL and anticipated that the Medical Assessor would assess his condition as a result of both injuries, with the relevant deemed date of injury being 22 August 2022. The Member in fact only referred the aggravation injury in the employ of TAL for assessment.
3. Mr Singh did not appeal the Member's finding.

1. The Medical Assessor set out a detailed history of the onset of Mr Singh's injury. He said:

"Mr Singh said that from around May 2021 he developed depressed mood as well as the pre-existing anxiety symptoms. He withdrew socially and stopped going to the shops. Mr Singh describes feeling very unwell in October 2021 so he stopped work and took leave because of his health. He describes feeling very guilty that he was not there to help his colleagues, and he remained very motivated to return to work as soon as possible.

Despite time off work, he remained low in mood with high anxiety, his energy levels and motivation were low, and he had not returned to previous activities such as going to the gym several times each week. He was not meeting with his friends, and his general selfcare was reduced, and he was no longer careful with his diet. Mr Singh made a workers' compensation claim in October 2021 which was accepted.

In January 2022 Mr Singh returned to work on a graduated basis and on lower stress tasks. He describes persistent problems with his concentration in the workplace and that he was forgetful. His sleep was poor, and he would have "brain fog" the following day. His mood continued low, and he continued to have a range of anxiety symptoms psychologically with excessive worry, and physiologically with breathlessness, physical restlessness and shaking. Mr Singh's hours at work were progressively increased back to full-time though he remained on low stress tasks. He continued to have a pervasive low mood and lack of pleasure in activities.

At the start of August 2022 there was a change of employer as TAL took over the business from Westpac. Mr Singh describes having an increase in his workload following this and a decrease in management support. Mr Singh's anxiety increased with the need to meet new people and adjust to the new business. His mental health declined, and he ceased work on August 30, 2022. He has not returned to work since, and his employment was terminated on 21 November 2023."

1. The Medical Assessor described Mr Singh's treatment and his symptoms. He recorded that Mr Singh had first sought treatment in May 2021 and been referred to a psychiatrist, Dr Saeed, in April 2022. He said:

"Mr Singh ceased work in August 2022 due to worsening symptoms indicating an aggravation of his major depressive disorder with anxious distress."

1. The Medical Assessor set out the history he obtained of Mr Singh's social activities and activities of daily living. He described his findings on the mental state examination in detail. Summarising the injuries and diagnoses he said:

"Mr Singh is a 36-year-old married man who lives with his mother, wife and their 5-year-old daughter. He developed his first major depressive episode with anxious distress during 2021 while employed by Westpac/BT Financial and had an accepted Workcover claim for that injury. This was aggravated in August 2022 when employed by TAL. Mr Singh's psychological injury has persisted and following the DSM-5TR system his diagnosis is of persistent depressive disorder with anxious distress with persistent major depressive episode which is severe without psychosis."

1. In answer to the question in the standard MAC template about whether any proportion of the impairment was due to a previous injury or condition, the Medical Assessor said:

"Yes. The workplace injury deemed to have occurred on 22 August 2022 is an aggravation of a previous psychological injury sustained on 28 May 2021."

1. The Medical Assessor undertook an assessment under the PIRS, based on his examination findings. He assessed Mr Singh in class 2 for each of self care and personal hygiene, social and recreational activities, travel, and social functioning. He assessed him in class 3 (moderate impairment) for concentration, persistence and pace and class 5 (totally impaired) for employability. Those scores convert to 9% WPI.
2. In the body of the MAC, the Medical Assessor described the medical records in the file in detail. Based on that material, he undertook a PIRS assessment as at the date Mr Singh's employment was transferred to TAL. He assessed Mr Singh in class 1 for self care and personal hygiene, class 2 for travel, social functioning, and employability, class 3 for social and recreational activities, and concentration, persistence and pace. Those scores convert to 7% WPI. The Medical Assessor certified 2% WPI resulting from the injury in the employ of TAL.
3. The Medical Assessor said that the previous relevant injury Mr Singh suffered was:

"Major depressive disorder with anxious distress. This disorder developed during 2021. There was a Workers Compensation claim made in October 2021 and Mr Singh had a period of 3 months away from work due to his health."

1. Explaining his reasons for the deduction, the Medical Assessor said:

"Mr Singh's current symptoms have persisted since development from around March 2021. They have varied in intensity and have affected his degree of function depending on that severity. He experienced an exacerbation of his major depressive disorder with anxious distress in August 2022. The details of Mr Singh's impairment due to the pre-existing major depressive disorder with anxious distress which was present at the time of his workplace injury is detailed in the attached PIRS worksheet.

I calculate that the deductible proportion due to the pre-existing major depressive disorder with anxious distress is 7%."

1. The Medical Assessor undertook two assessments of permanent impairment as he was required to do by paragraph 11.10 of the Guidelines (see Mathieson v Baptistcare New South Wales & ACT).[8]

1. Mr Singh's first ground of appeal was that the Medical Assessor did not give reasons for his s 323 deduction, for assigning "lower" ratings for concentration, persistence and pace and employability and for his divergence from other medical opinions.
2. The MAC shows that the Medical Assessor read and understood the Member's decision and made an assessment of the injury referred to him, being only the aggravation in the employ of TAL. Mr Singh's submissions suggest a lack of understanding of the decision when they refer to there being no psychological condition before his employment with the respondents, confirming that Mr Singh or his representatives believed that what was referred to the Medical Assessor was a disease injury which encompassed both periods of employment. That is contrary to the clear words of the Member's decision.
3. The second example of the alleged failure by the Medical Assessor to provide clarity is in the assessments of concentration, persistence and pace and employability. We do not agree that the Medical Assessor assigned "lower" impairment ratings. Consistent with the Medical Assessor's finding that Mr Singh was totally incapacitated for work, the Medical Assessor assessed him in class 5 for employability as at the date of his examination. The Medical Assessor assessed Mr Singh with a moderate impairment of concentration, persistence and pace. His assessments under those tables were the same as those made by Dr Anwar and Dr Khan.
4. The Medical Assessor's assessment for concentration, persistence and pace was the same in both of his PIRS assessments - class 3. A moderate impairment is significant, the examples in the Guidelines being that a person is unable to read more than newspaper articles or follow complex instructions.
5. The Medical Assessor said that after the injury in the employ of TAL:

"Mr Singh struggles to concentrate on material when reading to his daughter and estimates that he will persist with reading for up to 25 minutes. He uses task lists and reminders on his phone to assist his memory for everyday chores. He struggles to make arrangements such as for travel during recent family holidays. His motivation is low and he struggles to persist on intellectually demanding tasks."

1. The Medical Assessor set out his reasons for assessment in class 3 before Mr Singh commenced with TAL:

"Though Mr Singh was working before the injury of 22 August 2022 he was experiencing persistent problems with his concentration and memory such that he had not returned to full duties. He was experiencing daily 'brain fog'. Dr Saeed reports in April 2022 that Mr Singh's cognitive ability has declined. She reports that Mr Singh alluded that he is prone to make mistakes and that he often forgets things and has to set multiple reminders."

1. The Medical Assessor gave clear reasons for his assessments and did not provide a "lower" assessment.
2. The third example of the alleged failure by the Medical Assessor to give reasons is in respect of his "lack of explanation for diverging assessments". This example overlaps with ground 2 and we deal with the relevance of other opinions to the Medical Assessor's task below. We observe that the Medical Assessor summarised the reports of Mr Singh's treating psychiatrists, Dr Saeed, his psychologist and his general practitioner.
3. The Medical Assessor noted the opinion of Dr Khan, retained by Mr Singh's solicitors and observed that;

"In his report of 12 August 2024 Dr Khan confirms his opinion that Mr Singh's major depressive disorder commenced during his employment with Westpac/BT Financial and employment during the TAL period had a continuing aggravating effect."

1. The Medical Assessor also commented on Dr Anwar's opinion:

"In his report of 28 June 2024, Dr Anwar confirms his belief that the cause of the Mr Singh's psychological symptoms resulting in work incapacity on 29 August 2022 was employment with TAL Services Limited. Dr Anwar believes that the injury of May 2021 materially contributed to his permanent impairment."

1. In those comments, the Medical Assessor conveyed that he had considered the reports and that he understood that the assessments were based on different findings as to the cause of the injury to those referred to him.
2. The Medical Assessor noted the assessments of Dr Bisht and Dr Verma, and of Dr Hoey-Thompson, who saw him at the request of TAL to consider his fitness for employment.
3. The Medical Assessor gave reasons to support his assessment based on the referral made, being only in respect of the aggravation injury suffered in the employ of TAL. He did not apply incorrect criteria or make a demonstrable error.

1. The references to "the Review Panel" in Mr Singh's submissions convey some confusion about our role as an Appeal Panel and the review process under the Motor Accidents legislation. The submission that the assessment is "incorrect in a material respect" confirms that misunderstanding, as that test is relevant only in respect of a motor accident. A review panel under the Motor Accidents legislation may be required to determine questions of causation and, in that context, be required to consider the evidence in the file in detail. As Basten AJ pointed out in Lancaster v Foxtel Management Pty Ltd,[9] the statutory function is materially different.
2. An Appeal Panel convened under the 1998 Act is required to determine if the Medical Assessor applied incorrect criteria or made a demonstrable error. Because he assessed Mr Singh under the PIRS, the Medical Assessor has not applied incorrect criteria. A demonstrable error is an error which is apparent from an examination of the MAC.[10] As the Court of Appeal said in Burton, we are limited to considering any errors relied in Mr Singh's submissions.
3. The principles of assessment in paragraph 1.6 of the Guidelines include that the Medical Assessor is to assess a worker as he or she presents on the day of assessment, using the Medical Assessor's own clinical judgement.
4. Mr Singh said that the "preponderance of opinion" would favour adopting the 19% WPI assessed by Dr Anwar and Dr Khan. Dr Khan examined Mr Singh once in September 2023, more than 18 months before the Medical Assessor. Dr Anwar last examined Mr Singh in May 2024, one year before the Medical Assessor. The functioning observed on those dates may not be the same as on the day of the assessment by the Medical Assessor.
5. Importantly, the Medical Assessor was not required to adopt or choose between the other opinions in the file and is required to form his or her own opinion. In State of New South Wales (NSW Department of Education) v Kaur[11] Campbell J said:

"In Wingfoot Australia Partners Pty Ltd v Kocak [2013] HCA 43; 252 CLR 480, the High Court of Australia dealt with the nature of the jurisdiction exercised by a medical panel under cognate Victorian legislation. The legislation is not entirely the same but it is broadly similar in purpose. Allowing for some differences, the High Court said at page 498 [47]:

'The material supplied to a medical panel may include the opinions of other medical practitioners, and submissions to the Medical Panel may seek to persuade the Medical Panel to adopt reasoning or conclusions expressed in those opinions. The Medical Panel may choose in a particular case to place weight on the medical opinion supplied to it in forming and giving its own opinion. It goes too far, however, to conceive of the functions of the panel as being either to decide a dispute or to make up its mind by reference to completing contentions or competing medical opinions. The function of a medical panel is neither arbitral or adjudicative: It is neither to choose between competing arguments nor to opine on the correctness of other opinions on that medical question. The function is in every case to perform and to give its own opinion on the medical question referred to it by applying its own medical experience and its own medical expertise.'

Not all of this, as I have said, is apposite in the context of the New South Wales legislation. In particular, it is obvious that approved medical specialists are required to decide disputes referred to them by the process of medical assessment. Even so, it is not necessary that approved medical specialists should sit as decision makers choosing between the competing medical opinions put forward by the parties. Essentially, the function is the same as that described by the High Court in Wingfoot Australia. That is to say, their function is in every case to form and give his or her own opinion on the medical question referred by applying his or her own medical experience and his or her own medical expertise. It is sufficient, as their Honours pointed out at [55], that:

'The statement of reasons... explain the actual path of reasoning in sufficient detail to enable the Court to see whether the opinion does or does not involve any error of law'."

1. The Medical Assessor is directed by the standard MAP template to comment on other opinions and provide the reasons why his or her opinion differs. That is so the parties understand how and why a different result was reached, not because the Medical Assessor is required to agree with or choose between the previous assessments. The fact that another assessor made a different observation on a different day should not influence the Medical Assessor's opinion.
2. Apart from the reference to concentration, persistence and pace and employability in the submissions in support of the first ground of appeal concerning reasons, Mr Singh did not submit that the Medical Assessor had made errors in his assessment of his current functioning under the PIRS. We observe that the only difference between the assessments of Drs Khan and Anwar and that of the Medical Assessor is in the assessment of social and recreational activities. Drs Khan and Anwar assessed him in class 3 and the Medical Assessor assessed him in class 2.
3. The measurement of impairment under the PIRS is described in paragraphs 11.13 to 11.20 of the Guidelines. An assessor is required to determine the median class score - by arranging the scores under the tables of the PIRS in ascending order and averaging the two middle scores (paragraph 11.14) - and the aggregate score. Table 11.7 is used to convert those scores to WPI.
4. The assessments of Drs Anwar and Khan convert to a median class score of 2.5, rounded to 3 and an aggregate score of 17. The Medical Assessor's scores convert to a median class score of 2 and an aggregate of 16. Table 11.7 clearly shows the impact of that difference on the assessment of WPI.
5. The Medical Assessor did not make a demonstrable error in his consideration of other medical reports.
6. For those reasons, we have determined that the MAC issued on 7 May 2025 should be confirmed.

[1] [2025] NSWPIC 73.

[2] [2019] NSWCA 321.

[3] [2021] NSWCA 56.

[4] [2006] NSWCA 284.

[5] [2021] NSWCA 304 at [26].

[6] (1990) 10 MVR 570.

[8] [2025] NSWSC 213.

[9] [2022] NSWSC 929 at [35].

[10] Pitsonis v Registrar of the Workers Compensation Commission [2008] NCWCA at [49].

[11] [2016] NSWSC 346.