On November 10, 2016, the Supreme Court of Canada handed down a divided (four-to-three decision) in a medical malpractice case, which involved statistical evidence, or rather probabilistic inference. Benhaim v. St-Germain, 2016 SCC 48 (Nov. 10, 2016).  The case involved an appeal from a Quebec trial court, and the Quebec Court of Appeal, and some issues peculiar to Canadian lawyers. For one thing, Canadian law does not appear to follow lost-chance doctrine outlined in the American Law Institute’s Restatement. The consequence seems to be that negligent omissions in the professional liability context are assessed for their causal effect by the Canadian “balance of probabilities” standard.

The facts were reasonably clear, although their interpretation were disputed. In November 2005, Mr. Émond was 44 years old, a lifelong non-smoker, and in good health. At his annual physical with general practitioner Dr. Albert Benhaim, Émond had a chest X-ray (CXR). Benhaim at 11, ¶ 6. Remarkably, neither the majority nor the dissent commented upon the lack of reasonable medical necessity for a CXR in a healthy, non-smoking 40-something male. Few insurers in the United States would have paid for such a procedure. Maybe Canadian healthcare is more expansive than what we see in the United States.

The radiologist reviewing Mr. Émond’s CXR reported a 1.5 to 2.0 cm solitary lesion, and suggested a review with previous CXRs and a recommendation for a CT scan of the thorax. Dr. Benhaim did not follow the radiologist’s suggestions, but Mr. Émond did have a repeat CXR two months later, on January 17, 2006, which was interpreted as unchanged. A recommendation for a follow-up third CXR in four months was not acted upon. Benhaim at 11, ¶ 7. The trial court found that the defendant physicians deviated from the professional standard of care, a finding from which there was no appeal.

Mr. Émond did have a follow-up CXR at the end of 2006, on December 4, 2006, which showed that the solitary lung nodule had grown. Follow up CT and PET scans confirmed that Mr. Émond had Stage IV lung cancer. Id.

The issues in controversy turned on the staging of Mr. Émond’s lung cancer at the time of his first CXR, in November 2005, the medical consequences of the delay in diagnosis. Plaintiffs presented expert witness opinion testimony that Mr. Émond’s lung cancer was only Stage I (or at most IIA), at initial radiographic discovery of a nodule, and that he was at Stage III or IV in December 2006, when CT and PET scans confirmed the actual diagnosis of lung cancer. In the view of plaintiff’s expert witnesses, the delay in diagnosis, and the accompanying growth of the tumor and change from Stage I to IV, dramatically decreased Émond’s chance of survival. Id. At 13, ¶15-16. Indeed, plaintiff’s expert witnesses opined that had Mr. Émond been timely diagnosed and treated in November 2005, he probably would have been cured.

The defense expert witness, Dr. Ferraro, testified that Mr. Émond’s lung cancer was Stage III or IV in November 2005, when the radiographic nodule was first seen, and his chances of survival at that time were already quite poor. According to Dr. Ferraro, earlier intervention and treatment would probably not have been successful in curing Mr. Émond, and the delay in diagnosis was not a cause of his death.

The trial court rejected plaintiffs’ expert witnesses’ opinions on factual grounds. These witnesses had argued that Mr. Émond’s lung cancer was at Stage I in November 2005 because the lung nodule was less than 3 cm., and because Mr. Émond was asymptomatic and in good health. These three points of contention were clearly unreliable because they were all present in January 2007, when Mr. Émond was diagnosed with Stage IV cancer, according to all the expert witnesses. Every point cited by plaintiffs’ expert witnesses in support of their staging failed to discriminate Stage I from Stage III. In Her Honor’s opinion, the lung cancer was probably Stage III in November 2005, and this staging implied a poor prognosis on all the expert witnesses’ opinions. The failure to diagnose until late 2006 was thus not, on the “balance of probabilities” a cause of death. Id. At 15, ¶21.

The intermediate appellate court reversed on grounds of a presumption of causation, which comes into being when the defendant’s negligence interferes with plaintiff’s ability to show causation, and there is some independent evidence of causation to support the case. I will leave this presumption, which the Supreme Court of Canada held inappropriate on the facts of this case, to Canadian lawyers to debate. What was more interesting was the independent evidence adduced by plaintiffs. This evidence consisted of statistical evidence in the form of generality that 78 percent of fortuitously discovered lung cancers are at Stage I, which in turn is associated with a cure rate of 70 percent. Id. at 18 ¶30.

The plaintiffs’ witnesses hoped to apply this generality to this case, notwithstanding that Émond’s nodule was close to 2 cm. on CXR, that the general statistic was based up more sensitive CT studies, and that Émond had been a non-smoker (which may have influenced tumor growth and staging). Furthermore, there was an additional, ominous finding in Mr. Émond’s first CXR, of hilar prominence, which supported the defense’s differentiation of his case from the generality of fortuitously discovered (presumably small, solitary lung nodules without hilar involvement). Id. at 44 ¶83.

The trial court rejected the inference from the group statistic of 70% survival to the conclusion that Mr. Émond had a 70% probability of survival. Tellingly, there was no discussion of the variance for the 70% figure; nor any mention of relevant subgroups. The Court of Appeals, however, would have turned this statistic into a binding presumption by virtue of accepting the 78 percent as providing strong evidencec that the 70% survival figure pertained to Mr. Émond. The intermediate appellate court would then have taken the group survival rate as providing a more likely than not conclusion about Mr. Émond, while rejecting the defense expert witness’s statistics as mere speculation. Id. at 36 ¶67.

Adopting a skeptical stance with respect to probabilistic evidence, the Supreme Court reversed the Quebec Court of Appeal’s reversal of the trial court’s judgment. The Court cited Richard Wright and Jonathan Cohen’s criticisms of probabilistic evidence (and Cohen’s Gatecrasher’s Paradox), and urged caution in applying class or group statistics to generate probabilities that class members share the group characteristic.

“Appellate courts should generally not interfere with a trial judge’s decision not to draw an inference from a general statistic to a particular case. Statistics themselves are silent about whether the particular parties before the court would have conformed to the trend or been an exception from it. Without an evidentiary bridge to the specific circumstances of the plaintiff, statistical evidence is of little assistance. For this reason, such general trends are not determinative in particular cases. What inferences follow from such evidence — whether the generalization that a statistic represents is instantiated in the particular case — is a matter for the trier of fact. This determination must be made with reference to the whole of the evidence.”

Benhaim at 39, ¶74, 75 (internal citations omitted).

To some extent, the Supreme Court’s comments about statistical evidence were rather wide of there mark. The 78% statistic was based upon a high level of generality, namely all cases, without regard for the size of the radiographically discovered lesion, the manner of discovery (CXR versus CT), presence or absence of hilar pathology, or group or individual’s smoking status. In the context of the facts of the case, however, the trial court clearly had a factual basis for resisting the application of the group statistic (78% fortuitously discovered tumors were Stage I with 70% five-year survival).

The Canadian Supreme Court seems to have navigated these probabilistic waters fairly adeptly, although the majority opinion contains broad brush generalities and inaccuracies, which will, no doubt, show up in future lower court cases. For instance:

“This is because the law requires proof of causation only on a balance of probabilities, whereas scientific or medical experts often require a higher degree of certainty before drawing conclusions on causation (p. 330). Simply put, scientific causation and factual causation for legal purposes are two different things.”

Benhaim at 24, ¶47. The Court cited legal precedent for its observation, and not any scientific treatises. And then, the Supreme Court suggested that all one needs to prevail in a tort case in Canada is a medical expert witness who speculates:

“Trial judges are empowered to make legal determinations even where medical experts are not able to express an opinion with certainty.”

Benhaim at 37, ¶72. Clearly dictum on the facts of Benhaim, but it seems that judges in Canada are like those in the United States. Black robes empower them to do what mere scientists could not do. If we were to ignore the holding of Benhaim, we might think that all one needs in Canada is a medical expert who speculates.