Although not a medical claim, Carangelo v State of New South Wales  NSWCA 126 is of interest for its consideration of causation issues, including the factual causation, increased risks, material contribution and the scope for application of the exceptional case provision. The court (at ) found that this was not an exceptional case, having referred (at ) to the examples in the Review of the Law of Negligence on that issue.
Factual background, as per the headnote
Mr Carangelo, the appellant, suffered psychiatric injury whilst employed as a police officer in the New South Wales Police Force, being under the ultimate control and management of the Commissioner of Police (the Commissioner). Mr Carangelo complained that, in breach of a duty of care owed to him by the Commissioner (for whose actions the State of New South Wales, the respondent, was vicariously liable), the Commissioner failed to take reasonable precautions against the risk of his suffering psychiatric injury at two significant points in the course of his service. He claimed that if the Commissioner had taken appropriate steps at both points, specifically in offering pastoral care and support, and/or recommending him to a private psychiatrist, he would not have suffered Chronic Adjustment Disorder, anxious and depressed moods and other psychiatric disorders (the Psychiatric Injury).
….Whilst the primary judge found that though there were breaches of the relevant duty of care by the Commissioner at the two times identified, Mr Carangelo had failed to establish that the Commissioner’s breaches had caused or contributed to the Psychiatric Injury, which was instead caused by the experiences of Mr Carangelo as a police officer.
Mr Carangelo appealed from the primary judge’s orders, bringing three grounds of appeal contending misapplication of s 5D of the Civil Liability Act 2002(NSW), regarding the finding of no causation having been established…..
Findings , drawn from the headnote
Held, per Emmett AJA (Macfarlan and Gleeson JJA agreeing at  and  respectively), dismissing the appeal:
In relation to grounds 1 and 2:
(1) Causation pursuant to s 5D requires proof by the person seeking compensation that the negligent act or omission caused the loss or injury constituting the damage. All that is necessary is that, according to the course of common experience, the more probable inference appearing from the evidence is that a defendant’s negligence caused the injury or harm. In that context “more probable” means no more than that, upon the balance of probabilities, such an inference might reasonably be considered to have some greater degree of likelihood. It does not require certainty. 
Tabet v Gett  HCA 12; 240 CLR 537
(2) Causation in tort is not established merely because the allegedly tortious act or omission increased a risk of injury. , 
Amaca Pty Limited v Booth  HCA 53; 246 CLR 36
(3) The “but for” criterion of causation can be troublesome in different situations in which multiple acts or events lead to injury of a plaintiff. It is sufficient for the plaintiff to prove that the negligence of the defendant caused or materially contributed to the injury. What must be established is that the defendant’s conduct was responsible for an adverse difference in the plaintiff’s condition and its negligence was a cause of that difference. , 
Amaca Pty Limited v Booth  HCA 53; 246 CLR 36
(4) In some cases, although the relative contribution of two more factors to the particular harm can be determined, it may be that each factor is part of a set of conditions necessary to the occurrence of that harm. The limitations of the “but for” analysis of factual causation include cases in which there is more than one sufficient condition to the occurrence of the plaintiff’s injuries. Under the common law, each sufficient condition may be treated as an independent cause of the injuries. 
Strong v Woolworths Ltd  HCA 5; 246 CLR 182
(5) The evidence of the medical experts did not support the conclusion that it was more likely than not that there would have been a different outcome had the breaches of duty not occurred. The evidence clearly established that the Psychiatric Injury was caused by the severe stressors that Mr Carangelo experienced during his time in the police force. , 
(6) The question, with respect to the events of 1999, was whether the Psychiatric Injury would have been prevented or, possibly, alleviated to a significant degree, by referral to a police medical officer and private psychiatrist in 1999. , 
(7) The question, with respect to the events of 2005, was whether it is more likely than not that, had Mr Carangelo been afforded forewarning, and appropriate support when the stress of PIC investigation arose, his Psychiatric Injury would have been avoided or would have been less serious. , 
(8) The evidence did not support a finding, on the balance of probabilities, that such actions would have resulted in a relevant difference so far as Mr Carangelo’s Psychiatric Injury is concerned. It indicated no more than Mr Carangelo may have lost a chance of avoiding or ameliorating the Psychiatric Injury. That being the conclusion of the primary judge, there was no error on her Honour’s part in reaching that conclusion and in entering judgment for the State. , , , 
In relation to ground 3:
(9) Negligent conduct that materially contributes to a plaintiff’s harm, but which cannot be shown to be a necessary condition of its occurrence may, in accordance with established principles, be accepted as establishing factual causation, subject to the normative considerations to which s 5D(2) requires that attention be directed. 
(10) This is not a case where there were various factors all of which may have, in some way, contributed to the Psychiatric Injury. The evidence is clear that the Psychiatric Injury was caused by the various stressors to which Mr Carangelo was subjected in the course of the performance of his duties as a police officer over many years. Section 5D(2) cannot be called in aid simply because there is no evidence to support a contention as to the causation of injury. 
(11) This is not an exceptional case, such that responsibility for the harm suffered by Mr Carangelo should be imposed upon the State as vicariously liable for the conduct of the Commissioner. ,