Statistically Significant Evidence – A Cause for Success
June 30, 2016 By: Christopher C. Rootham Read Time: 3 minutes
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In British Columbia (Workers’ Compensation Appeal Tribunal) v. Fraser Health Authority, seven technicians at a single hospital laboratory were diagnosed with breast cancer. Each of them applied for compensation under British Columbia’s Workers Compensation Act (“the Act”) on the basis that the cancer was an occupational disease. The payment of benefits under the Act is conditional upon the employment having been of “causative significance” in the development of the worker’s illness.

The medical experts in that case confirmed that the number of breast cancer diagnoses (7 of the 63 workers studied) represented a statistically significant cluster, with a “standardized incidence ratio” for breast cancer approximately eight times the rate that would have been expected in the general population. Ultimately, however, the medical experts did not reach “scientific conclusions to support the association between work-related exposures and breast cancer in this cluster.”

A review officer of the Workers’ Compensation Board denied each of the claims, finding that “there is insufficient evidence… to conclude that [each worker’s] years of employment as a medical lab technician has played a significant role in causing breast cancer.” On appeal to the Workers’ Compensation Appeal Tribunal, the Tribunal concluded that the Board applied a too stringent standard of proof by requiring scientific certainty. The Tribunal concluded that it was not necessary to identify a specific causal agent, it being sufficient for the evidence merely to point to a causal link between a disease and an occupation. Here, the evidence of past carcinogenic exposure, coupled with the statistically significant cluster of breast cancer cases among laboratory workers, comprised “positive evidence” supporting a conclusion that it was as likely as not that the workers’ breast cancer was caused by workplace exposure.

The employer applied to the Tribunal for reconsideration of its decision. The Tribunal has the authority to reconsider a decision “to cure a jurisdictional defect”. The employer argued that such a defect existed, since the Tribunal’s finding, in its original decision of a causal link between the workers’ breast cancer and their employment, lacked supporting evidence and was, as such, patently unreasonable. The Tribunal agreed to reconsider its decision on that basis, but nevertheless concluded that its previous decision was not patently unreasonable.

On eventual appeal to the Supreme Court of Canada, the Tribunal’s initial decision was upheld. The Court, however, agreed with the majority of the BC Court of Appeal that the reconsideration decision was a nullity.

The Court acknowledged that the Act states that where the evidence is evenly weighted on causation, that issue must be resolved in the worker’s favour. This represents an important distinction from civil tort claims, where causation must always be established on a balance of probabilities. However, the Court concluded that the important issue in this case was not the lower statutory burden of proof, but “how causation – irrespective of the standard of proof – may be inferred from evidence.” The Court went on to conclude that a tribunal may rely upon statistical evidence alone in determining causation, stating that:

“causation can be inferred – even in the face of inconclusive or contrary expert evidence – from other evidence, including merely circumstantial evidence. This does not mean that evidence of relevant historical exposures followed by a statistically significant cluster of cases will, on its own, always suffice to support a finding that a worker’s breast cancer was caused by an occupational disease. It does mean, however, that it may suffice. Whether or not it does so depends on how the trier of fact, in the exercise of his or her own judgment, chooses to weigh the evidence.


In this case, the statistical evidence – that 7 of 63 workers were diagnosed with cancer, and that this was eight times the rate in the general population – was a sufficient justification for the Tribunal’s decision.

On the issue of the Tribunal’s power of reconsideration, the Court simply confirmed the BC Court of Appeal’s conclusion that the power to reconsider on jurisdictional grounds did not include the power to reconsider if the decision was patently unreasonable. Rather, the power to reconsider in order to “cure a jurisdictional defect” was no broader than the common-law right to reconsider a decision, as set out in Chandler v. Alberta Association of Architects: to correct non-substantive slips and errors that result in the tribunal not exercising the jurisdiction it has been given.

The decision in Fraser Health Authority is an important case about the use of statistical evidence to demonstrate causation in any proceeding – be it workers’ compensation, human rights, or a civil court action. It also severely restricts the ability of administrative tribunals to reconsider their decisions when their constituting statutes only grant the power to reconsider on jurisdictional grounds. Such a power is not an invitation to revisit the merits of the case, but only to ensure that the tribunal at first instance actually addressed the entire case before it.

This content is not intended to provide legal advice or opinion as neither can be given without reference to specific events and situations. © 2018 Nelligan O’Brien Payne LLP.

Service: Employment Law