Causation - Statistical. Levac v. James
In Levac v. James (Ont CA, 2023) the Court of Appeal considered what can be called 'statistical causation':
 After recounting the traditional “but for” test for causation, the trial judge referred to the “material contribution to risk” test as clarified in Clements v. Clements, 2012 SCC 32,  2 S.C.R. 181. However, reading that paragraph of his reasons in context, I understand the trial judge to be saying that Dr. James’ breach of IPAC need not be the sole cause of the infections, but merely a “contributing” one under the but for analysis, rather than applying the material contribution test that is theoretically available in situations where proof of causation is otherwise impossible. This did not affect the outcome here, much like in Moran v. Fabrizi, 2023 ONCA 21, at para. 17, where the trial judge superfluously referred to the material contribution test, but this did not amount to a reversible error as causation was otherwise proven. See also Donleavy v. Ultramar Ltd., 2019 ONCA 687.
 I also see no error in the trial judge’s conclusion that causation was proven in respect of the Genetically Linked Patients, based on the genetic match between the CC59 strain colonizing Dr. James (and only Dr. James) and infecting some of his patients (and only his patients), the expert evidence pointing to his substandard IPAC as the source of transmission, and the lack of a viable alternative explanation for the genetic match, relying on case law including Snell v. Farrell, 1990 CanLII 70 (SCC),  2 S.C.R. 311, and Hassen v. Anvari, 2003 CanLII 1005 (Ont. C.A.), leave to appeal refused,  S.C.C.A. No. 490.
 For the remaining patients, the trial judge treated the statistical evidence as a basis to infer causation in negligence. He explained as follows:
The Supreme Court has also instructed that causation may be inferred from evidence, including from circumstantial evidence. This is so even where the record contains inconclusive or contrary expert evidence, provided that the inference takes into account all of the available evidence and is reasonable in the circumstances. Thus, for example, in analyzing a claim that exposure to carcinogens at a plaintiff’s employment caused a plaintiff’s cancer, the Court has indicated that evidence of “historical exposures followed by a statistically significant cluster of cases” can suffice to satisfy the causation requirement: British Columbia (Workers’ Compensation Appeal Tribunal) v. Fraser Health Authority, 2016 SCC 25 (CanLII),  1 SCR 587, at para 38. Causation can therefore be discerned by inference from the statistical evidence. [Emphasis added.] Dr. James relies on statements from other cases advising caution in using statistical evidence to establish causation: see e.g., Andersen, at paras. 393-95; Benhaim v. St-Germain, 2016 SCC 48,  S.C.R. 352, at paras. 74-76. Here, the statistical evidence was not relied upon to establish causation in respect of a single individual, but rather to establish an inference across the entire Class, adding to these dangers.
 Ms. Levac asserts that there is no bar to a court relying on statistical evidence of causation, and that such reliance has been accepted at least since Rothwell v. Raes (1988), 1988 CanLII 4636 (ON SC), 66 O.R. (2d) 449 (H.C.).
 While correlation is not scientific causation, scientific certainty is not required for legal proof: Snell, at pp. 330-31; Benhaim, at para. 47. The trial judge had the benefit of extensive expert evidence on the relationship between proper IPAC and infection rates. He found that the risk of serious infection among Dr. James’ patients was staggering – at least 49 times higher than expected – and concluded that the statistical evidence was “so overwhelming that it cannot be ignored.”
 As Wagner J. (as he then was) stated in Benhaim, at para. 78, deference is owed to trial judges when drawing inferences of causation based on statistics:
Drawing an inference from a general statistic in a particular case is an inherent, and often implicit, part of the fact-finding process. A statistic alone reveals nothing about a particular case. It must be interpreted in light of the whole of the evidence. This interpretation is the role of the trial judge, and it is entitled to considerable deference on appeal. Respectfully, the Court of Appeal in this case failed to show such deference. In this case, there was powerful circumstantial evidence on which to conclude that a statistical association represented a causal link on a balance of probabilities. The trial judge further found that Dr. James had not put forward a viable, non-negligent explanation for the outbreak as a whole.
 The trial judge’s common finding on specific causation includes the important caveat, “absent sufficient evidence to the contrary.” In this way, he recognized that the ultimate determination of whether a Class Member was infected because of Dr. James’ breaches remains an individual issue. This does not shift the onus or burden of proof. Rather, at individual trials, each Class Member still must prove their case on a balance of probabilities. However, they will be able to rely on the trial judge’s common findings, including that the infections among the non-Genetically Linked Patients are presumptively attributable to Dr. James’ substandard IPAC. As the trial judge explained:
While each Class member will have to demonstrate their right to a claim by showing that they partook of this common risk and suffered consequences, the inference that their injury was specifically caused by Dr. James’ actions is statistically proven. As in Andersen, supra and [Buchan v. Ortho Pharmaceutical (Canada) Ltd. (1984), 1984 CanLII 1938 (ON SC), 46 O.R. (2d) 113, aff’d (1986) 1986 CanLII 114 (ON CA), 54 O.R. (2d) 92 (C.A.)], supra, the evidence before me demonstrates that the risk ratio of Dr. James’ epidural injections is well above 2.0, thus presumptively proving causation for class members (subject, of course, to any evidence which might emerge in an individual case rebutting this presumption). This approach is consistent with well-established causation principles in negligence generally, and medical negligence specifically, where the defendant is often in a better position than the plaintiff to determine the cause of an injury: see e.g., Snell, at paras. 328-29; Benhaim, at paras. 48-49. As the trial judge noted, the procedures here occurred literally behind each patient’s back.
 Furthermore, although the prima facie finding was made on a Class-wide basis, it remains open to Dr. James to rebut this inference in respect of individual non-Genetically Linked Patients, where such evidence exists. While the reality is that a complete finding of causation may be an evidentiary inevitability in most cases, that is not the same as a shift in onus.
 I see no error in the trial judge’s reliance on statistical evidence in drawing a Class-wide, rebuttable inference that Dr. James’ substandard IPAC caused the infections.
 Dr. James also argues that even if he breached the standard of care based on his failure to report, investigate, and remediate the first infection, the trial judge erred in drawing the rebuttable inference that these breaches caused the infections of the non-Genetically Linked Patients after August 7, 2010. In Dr. James’ view, there was no evidence that a material change in outcome would have occurred had he reported the first infection of which he became aware (which was itself seven months into the Class Period).
 I disagree that there was no evidence on which to find a different outcome would have resulted had Dr. James acted differently. Specifically, the trial judge reasoned that if Dr. James had reported the first infection, it was likely that the medical director would have addressed it in accordance with his professional obligations, as he did when the TPH investigation was launched. Either Dr. James would have improved his IPAC or the medical director would have caused him to do so. On this basis, it is unlikely the subsequent infections would have occurred. This conclusion was open to the trial judge on the record.
 For these reasons, I would dismiss this ground of appeal.