Law & Governance

Law & Governance November 0000 : 0-0

Causation and Scientific Evidence

Philip Spencer


[No abstract available for this article.]

I. Introduction

It is trite law that for a claimant to be successful in a product liability action s/he must not only demonstrate that the product was either negligently manufactured or designed or that there was a failure to warn but that that negligence, in fact, caused the claimant's loss. The issue of causation is at the heart of every product liability claim and is often the determinative issue that the trier of fact must ultimately decide. In most product liability cases, scientific expert evidence is admitted to determine the issue of causation. 1 Thus, products litigation is especially sensitive to the evolution of Canadian law with regard to the admission of scientific expert evidence.

Today our courts adjudicate in a world of rapidly expanding scientific knowledge. Science once viewed as controversial is now readily accepted and the scientific basis for that evidence has become well established. Having said that, novel and cutting-edge science is also finding its way into the courtroom more and more often. Expert evidence will constitute "novel science" where the scientific theory or technique relied on has not yet been generally accepted in the relevant field of endeavour, or where the particular use made of a generally accepted theory or technique has not yet been generally accepted in that field. 2 Over the past decade the law in Canada with regard to the admissibility of novel scientific expert evidence has evolved with the decisions of our highest court in R v. Mohan3 and R v. J.J. 4 The Supreme Court of Canada has rejected the "general acceptance" test and has replaced it with a case-by-case analysis of novel scientific evidence so as to ensure the requisite degree of reliability. Despite this evolution, some argue that procedurally we need to evolve further. In the United States it is possible to challenge the methodology and reasoning of an expert's evidence prior to trial on a summary judgement basis in what is known as a Daubert hearing. Because the Ontario Rules of Practice do not compel an expert to disclose their reasoning/methodology until trial, a challenge to expert testimony on a summary judgment motion is not practical in Canada prior to trial. It is not until the expert gives their evidence that the reasoning becomes apparent and then the issue is then no longer admissibility but weight.

This paper provides an overview of the principles of cause in fact, duty to warn, intermediate inspection, and intervening events as they apply to product liability matters. The paper also outlines the evolution of Canadian law with regard to the admissibility of novel scientific evidence, provides possible avenues for further evolution and improvement drawing on recent trends in both Canada and the United States, and comments on the American experience in this area.

II. Causation In Fact

In order to be successful in any product liability action, the plaintiff must establish, on a balance of probabilities, that a defect in the product's manufacture, design or warnings was, as a matter of fact, causally connected to the plaintiff's injury. 5 In other words, there must be some link or connection between the wrongful act and the loss being complained of. In Snell v. Farrell, 6 Sopinka J. defined causation as follows:

Causation is an expression of the relationship that must be found to exist between the tortious act of the wrongdoer and the injury to the victim in order to justify compensation of the latter out of the pocket of the former. 7

(a) Establishing Cause-in-Fact in a Product Liability Action

The case law reveals that there is no single test or approach which has been used to establish the causal requirement. 8 Generally speaking, judges do not want to see meritorious claims frustrated because of an inability to meet rigid or technical standards of proof. On the other hand, courts also want to ensure parties are not held liable where no reasonable connection links the defendant's conduct and the plaintiff's injuries. 9 As a result, the courts have, for the most part, adopted a common sense approach to this question.

(i) The Traditional Rule - The "But For" Test

According to traditional principles in the law of torts, the plaintiff must prove, on a balance of probabilities that, "but for" the defendant's tortious conduct, the plaintiff would not have sustained the injury or damage. 10 Lord Denning's statement in Cork v. Kirby Maclean Ltd.11 explains the test:

If you can say that the damage would not have happened but for a particular fault, then that fault is in fact a cause of the damage; but if you can say that the damage would have happened just the same, fault or no fault, then the fault is not a cause of the damage. 12

The traditional approach to causation came under attack in a number of cases in which there was concern that due to the complexities of proof of causation, the victim of tortious conduct would be deprived of relief. This concern is strongest in cases where the plaintiff is the likely victim of the combined tortious conduct of a number of defendants, but cannot prove causation against a specific defendant or defendants in accordance with traditional principles. 13In the product liability context, the challenge to the traditional approach manifests itself in cases in which a product which can cause injury, is widely manufactured and marketed by a large number of corporations or, as alluded to above, in situations where there were several possible causes of the plaintiff's injury. 14 This concern has led courts in other jurisdictions to reject traditional principles of causation in favour of more relaxed approaches. However, in Snell the Supreme Court of Canada resisted the adoption of alternative theories of liability for causation in favour of a more flexible and common sense application of the traditional rule.

(ii) Flexible Application of Traditional Principles

In Snell v. Farrell the Supreme Court of Canada considered the issue of whether the plaintiff must prove causation in accordance with traditional principles or whether recent developments in the law justified a finding of liability on the basis of some less onerous standard. While Snell was a medical malpractice action, its principles apply equally to product liability litigation. 15 Speaking for the court, Sopinka J. stated that the dissatisfaction with the traditional approach to causation lay not with the traditional rule, but with its application. The court held that the traditional principle was adequate if applied in a flexible manner. Sopinka J. stated:

I am of the opinion that the dissatisfaction with the traditional approach to causation stems to a large extent from its too rigid application by the courts in many cases. Causation need not be determined with scientific precision. It is … essentially a practical question of fact which can be best answered by ordinary common sense rather than abstract metaphysical theory. 16

Although Sopinka, J. did not expressly reject the traditional principles of causation in favour of a new, less onerous standard, he stated that if convinced that defendants who were substantially connected to the injury were escaping liability because plaintiffs were unable to prove causation under the traditional principle, he would not hesitate to adopt one of the alternatives. 17 As such, the holding of Snell has been interpreted to give judges, who see causation as a barrier in complicated product liability cases, room to accept alternative theories of liability. 18

(iii) Alternative Approaches: Establishing Cause in the Difficult Case

The flexibility afforded to judges to accept alternative theories of liability has resulted in the application of less onerous standards of proof with regard to causation in some cases. Athey v. Leonati19 dealt with a claim for negligence for injuries arising out of two motor vehicle accidents. The plaintiff had a history of back problems over a number of years. Several months following the accidents, the plaintiff suffered a herniated disk in his back while exercising, which required surgery. The issue was whether the herniated disk was caused by the accidents (and the negligence of the two drivers) or whether it was attributable to the plaintiff's pre-existing back condition. In finding the plaintiff was entitled to full damages, Major J. confirmed that the general test of causation is the but for test and that the test of causation need not be determined with scientific precision. 20 However, Major J. also recognized that the but for test is unworkable in some circumstances, for example, where the plaintiff's injuries emanate from "a myriad of other background events [or conditions] which were necessary preconditions" to the occurrence of the injuries in question. In such cases, it is frequently impossible to attribute a single cause to the plaintiff's injuries. For that reason, the Supreme Court has recognized that the traditional test for causation, the "but-for" test, is unworkable in some situations and, in those cases, should be replaced by the "material contribution" test, which is concerned with whether the defendant's negligence "materially contributed" to the occurrence of the plaintiff's injuries.

More recently, in Walker Estate v. York-Finch General Hospital21 the Supreme Court applied the material contribution test where it was found that the "but for" test would work unfairly for the plaintiff. In that case the plaintiff alleged that the Canadian Red Cross Society negligently screened blood donors which resulted in the plaintiff contracting HIV. Major J. held that in some cases the but for test is "unworkable" because it is "difficult or impossible" to apply. In these cases, the material contribution test was suggested. In defining the test Major J. stated that a defendant would be liable if its negligence materially contributed to the occurrence of the injury. The court referred to Athey where it was stated that a contributing factor was material if it falls outside the de minimus range. The Walker Estate decision demonstrates the court's willingness to apply alternative, less onerous theories of causation.

The trend toward the adoption of less onerous theories of causation continued in Meyers (Next friend of) v. Stanley. 22 In that case, the plaintiff parents sued their obstetrician for negligence in the care and delivery of their child. The court noted that often it is extremely difficult for the plaintiff to prove the cause of their injury. 23 The court went on to state that it is settled law that the plaintiff need not establish causation with scientific or medical certainty. In determining that causation was sufficiently established and the plaintiff was entitled to compensation, it was held that the evidence need only show that the negligence of the defendant materially contributed to the plaintiff's injury/loss.

(b) Conclusion

The general trend in the case law indicates that progressively, developments have led to a lessening of the burden facing a plaintiff trying to prove causation. We will have to wait and see the extent to which such a standard of causation is applied in the product liability context. If our courts apply this standard, it will lighten the plaintiff's task of establishing that a defendant's actions, whether they be negligent design, manufacture or a failure to warn, caused the plaintiff's injuries. This would result in defendant's in product liability actions being held liable in a greater number of cases where, for example, there is some inherent difficulty in proving causation with scientific accuracy, where the facts surrounding causation lie uniquely within the knowledge of the defendant manufacturer or distributor or where multiple causes give rise to loss.

III. The Duty To Warn

As a matter of common law, it is well established that a product manufacturer has a duty to warn consumers of dangers inherent in the use of the product of which it knows or has reason to know. This duty emanates from the neighbour principle which lies at the foundation of the law of negligence. The underlying rationale is that one who brings themselves into a relationship with another, through an activity which foreseeably exposes the other to danger if proper care is not observed, must exercise reasonable care to safeguard them from that danger. The duty of reasonable care commonly comprehends a duty to warn of danger, the breach of which will, when it is the cause of injury, give rise to liability. 24 Simply put, the duty to warn requires manufacturers to warn consumers of the risks associated with the reasonably foreseeable use of their products.

(a) The Scope of the Duty

The seminal case on the duty to warn is the Supreme Court of Canada's decision in Lambert v. Lastoplex Chemicals Co.25 In Lambert, the plaintiff engineer was seriously injured when fumes from the defendant's lacquer product exploded while the plaintiff was lacquering his basement. Before using the lacquer, the plaintiff turned his thermostat down to prevent the furnace from automatically engaging. However, because he did not extinguish the pilot light, an explosion occurred. Although the defendant's product contains several general warnings, it did not warn against using the lacquer near a lit pilot light. The court held that the defendant manufacturer's warnings were inadequate because they did not warn against specific dangers. Speaking for the majority, Laskin, J. defined the scope of the duty to warn as follows:

Manufacturers owe a duty to consumers of their products to see that there are no defects in manufacture which are likely to give rise to injury in the ordinary course of use. Their duty does not, however, end if the product, although suitable for the purpose for which it is manufactured and marketed, is at the same time dangerous to use; and if they are aware of its dangerous character they cannot, without more, pass the risk of injury to the consumer. Where manufactured products are put on the market for ultimate purchase and use by the general public and carry danger … the manufacturer, knowing of their hazardous nature, has a duty to specify the attendant dangers, which it must be taken to appreciate … A general warning, as for example, that the product is flammable, will not suffice where the likelihood of fire may be increased according to the surroundings in which it may reasonably be expected that the product will be used. The required explicitness of the warning will, of course, vary with the danger likely to be encountered in the ordinary use of the product. 26

In Buchan v. Ortho Pharmaceutical (Canada) Ltd., 27 the Ontario Court of Appeal expanded on these principles, noting:

Once a duty to warn is recognized, it is manifest that the warning must be adequate. It should be communicated clearly and understandably in a manner calculated to inform the user of the nature of the risk and the extent of the danger: It should be in terms commensurate with the gravity of the potential hazard, and it should not be neutralized or negated by collateral efforts on the part of the manufacturer. The nature and extent of any given warning will depend on what is reasonable having regard to all the facts and circumstances relevant to the product in question.

Returning to this issue in Hollis v. Dow Corning Corp., 28 the Supreme Court of Canada observed:

When manufacturers place products into the flow of commerce, they create a relationship of reliance with consumers, who have far less knowledge than the manufacturers concerning the dangers inherent in the use of the products, and are therefore put at risk if the product is not safe. The duty to warn serves to correct the knowledge imbalance between manufacturers and consumers by alerting consumers to any dangers and allowing them to make informed decisions concerning safe use of the product. 29

. . .

The nature and scope of the manufacturer's duty to warn varies with the level of danger entailed by the ordinary use of the product. Where significant dangers are entailed by the ordinary use of the product, it will rarely be sufficient for manufacturers to give general warnings concerning those dangers: The warnings must be sufficiently detailed to give the consumer a full indication of each of the specific dangers arising from the use of the product. 30

(b) The Continuing Duty to Warn

It should also be noted that the duty to warn is a continuous one requiring that manufacturers must not only be vigilant to warn their consumers of the dangers of which they are aware at the time of the sale, but they must also take steps to alert them when they discover dangers after the product has been sold and distributed.

In Rivtow Marine Ltd. v. Washington Iron Works and Walkem Machinery and Equipment Ltd., 31 the defendants designed, manufactured and installed cranes which were fitted on the "Rivtow Carrier", managed by the plaintiff. The defendants were aware of serious structural defects in the cranes several months prior to fitting the cranes on the barge of the plaintiff but had failed to warn the plaintiff. The majority of the court held:

The knowledge of the danger involved in the continued use of these cranes for the purpose for which they were designed carried with it a duty to warn those to whom the cranes had been supplied, and this duty arose at the moment when the respondents became seised with the knowledge. 32

In Buchan a 23-year-old plaintiff suffered permanent, partial paralysis from a stroke after taking oral contraceptives manufactured and distributed by the defendant and prescribed by her physician. Evidence at trial showed that reliable studies conducted prior to the plaintiff's stroke indicated that the risk of stroke to contraceptive users was significantly higher as compared to non-users. These studies, along with articles and reports, were published prior to the plaintiff's stroke, thereby putting the manufacturer on notice of the link between the use of the contraceptive and stroke. The Ontario Court of Appeal found that, given its awareness of the risk, the manufacturer owed a duty to consumers to furnish a timely warning commensurate with the risk and the gravity thereof.

(c) Establishing Causation Where a Failure to Warn is Alleged

Like any product liability action, where a breach of the duty to warn is alleged, the plaintiff must prove causation. In other words, the plaintiff must show that the defendant's negligent failure to warn was the cause of the plaintiff's loss. In order to show that the defendant's failure to warn was a causal factor in the plaintiff's loss, the plaintiff must show that s/he would have heeded a warning and taken a different course of action if it had been given. Under traditional principles of causation, the plaintiff would need to meet the "but for" test and establish that the injury would not have occurred but for the defendant's failure to warn. In most cases, the plaintiff will allege that indeed if a warning had been given that they would have taken a different course of action. However, such claims are made after the fact and with the benefit of hindsight and, thus, one may well question the reliability of such self-serving statements. 33

Faced with this problem, courts have had to decide whether to apply a subjective or objective test for determining whether the warning would have been heeded. In Reibl v. Hughes, 34 the Supreme Court of Canada held that an objective test should be used to determine causation where a failure to warn is alleged. Speaking for the court, Laskin, C.J.C. stated

It could hardly be expected that the patient who is suing would admit that he would have agreed to have the surgery, even knowing all of the accompanying risks. His suit would indicate that, having suffered serious disablement because of the surgery, he is convinced that he would not have permitted it if there had been proper disclosure of the risk, balanced by the risk of refusing the surgery.

Thus, the Supreme Court outlined that to show causation where a failure to warn is alleged in a medical malpractice action, the plaintiff must show that a reasonable patient, in the same circumstances, would not have had the surgery if adequate warnings had been provided. This "modified objective test" was preferred because it does not depend upon the plaintiff's evidence as to his or her state of mind, which may be affected by hindsight. It is not vulnerable to what may be viewed as unreliable and self-serving evidence from plaintiffs. 35

Despite this, the Ontario Court of Appeal rejected the use of Reibl's "modified objective test" of causation in product liability cases. As indicated, in Buchan the defendant pharmaceutical company was sued for failing to provide adequate warnings of the risk of stroke associated with the use of its contraceptive pill. The plaintiff suffered a stoke after taking the defendant's product. The Ontario Court of Appeal considered whether Reibl v. Hughes should apply where a manufacturer allegedly fails to provide adequate warnings and concluded that, while the Reibl test is applicable to appropriate medical malpractice cases, it is not appropriate for product liability cases. The court noted that:

As between drug manufacturer and consumer, the manufacturer is a distant commercial entity that, like manufacturers of other products, promotes its products directly or indirectly to gain consumer sales, sometimes, as in this case, accentuating value while underemphasizing risks. Manufacturers hold an enormous informational advantage over consumers and, indeed, over most physicians. The information they provide often establishes the boundaries within which a physician determines the risks of possible harm and the benefits to be gained by a patient's use of a drug. Manufacturers, unlike doctors, are not called upon to tailor their warnings to the needs and abilities of the individual patient, and, unlike doctors, they are not required to make the kind of judgment call that becomes subject to scrutiny in informed consent actions. 36

The Supreme Court of Canada revisited this issue in Hollis v. Dow Corning Corp., where the plaintiff sued a breast implant manufacturer for injuries she sustained when her implants ruptured. The majority of the Supreme Court of Canada adopted the Buchan analysis and rejected the objective test to prove causation in product liability cases - failure to warn cases, in favour of a subjective test. The reasoning for the subjective test in products cases was that a manufacturer can be expected to act in a more self-interested manner (compared to doctors). In the case of a manufacturer, therefore, there is a greater likelihood that the value of a product will be over-emphasized and the risk under-emphasized. It was, therefore, seen as highly desirable from a policy perspective to hold the manufacturer to a strict standard of warning consumers of dangerous side effects to these products. 37

(d) Conclusion

The test, then, is whether this particular plaintiff would have, in the circumstances, conducted himself or herself differently had an adequate warning been given. In effect, the Supreme Court in Hollis chose to adopt a form of strict liability as an incentive for pharmaceutical manufacturers to take extra care in providing full and complete disclosure of risks associated with their products. Hollis places manufacturers in a difficult position when defending warnings cases as a result of the fact that the decision arguably establishes strict liability as the standard where the duty of warn has been breached. Despite this, it remains to be seen whether the courts will apply Hollis to all warnings cases. Some have argued that the recent judgment of the Supreme Court of Canada in Walker Estate suggests that the holding of Hollis should be read as limited to cases of learned intermediaries. 38

IV. Intermediate Examination

Jurisprudence considering intermediate examination in the context of product liability is unsettled. The locus of the legal debate surrounds the proper delineation of when the defence of intermediate examination should be available to the manufacturer and how it affects the manufacturer's duty of care. Trends in recent case law suggest that the defence of intermediate examination should go to the apportionment of fault rather than to the absolute removal of the duty of care.

The duty of care in products liability is grounded in whether a manufacturer intends its products to be used by the ultimate consumer in the form in which they are left with no reasonable possibility of intermediate examination. As stated by Lord Atkin in Donoghue v. Stevenson, 39

…a manufacturer of products, which he sells in such form as to show that he intends them to reach the ultimate consumer in the form which they left him with no reasonable possibility of intermediate examination, and with the knowledge that the absence of reasonable care in the preparation or putting up of the products will result in an injury to the consumer's life or property, owes a duty to the consumer to take that reasonable care.

In determining whether a defence of intermediate examination is viable, Courts are thereby charged with the task of ascertaining the manufacturer's position at the time the product is released for distribution.

(a) Probability of Intermediate Examination

Goddard L.J., in Paine v. Colne Valley Electricity Supply Co. Ltd.40 engaged in a careful examination of the doctrines of intermediate examination and duty of care. Specifically, he analyzed Lord Atkin's use of the word "possibility" in the abovementioned passage. Goddard concluded that Atkin could not have intended to use the word "possibility" as it had no commercial application and that consequently, the word "probability" should be substituted. Interpreted broadly, and having consideration to Goddard's analysis, Atkin's excerpt infers that where a manufacturer foresees the reasonable probability of an intermediate examination, the manufacturer may avoid liability. This passage has not, however, been interpreted to entirely absolve the manufacturer of his duty of care. Rather, recent jurisprudence indicates that there remains an obligation on the manufacturer to take reasonable care to prevent defects that may not be discovered prior to the ultimate consumer's use even where an intermediate inspection is a reasonable probability.

(b) No Anticipation of Intermediate Examination

Where there is no reasonable probability of an intermediate examination, the manufacturer is held to the duty of care requiring it to take the degree of care necessary in all circumstances to prevent the risk of harm to another. 41Mathews v. Coca-Cola Co. of Canada Ltd.42 involved a situation where a waitress opened a bottle of Coca-Cola for her customer and the bottle contained a dead mouse. The court, in its decision affirmed the notion that where a product is so prepared as to be intended to be used immediately by the consumer in the form in which it left the manufacturer without the anticipation of an intermediate examination, the liability for any defect in that product will remain entirely with the manufacturer. Gillander, J.A. reasoned that even where an intermediate examination could have been conducted, the manufacturer would not necessarily be absolved of liability.

(c) Anticipation of Intermediate Examination

Where it is a reasonable certainty that an intermediate examination will occur, the manufacturer may be entitled to an absolute defence thereby absolving itself of liability. Theall states that,

Where, at the time a product is distributed, a manufacturer reasonably anticipates the consumer or an intermediate party will conduct an examination that would reveal a defect before the product is used or incorporated into another product, the manufacturer owes no duty of care.

Viridian Inc. v. Dresser Canada Inc.43 stands for the above stated proposition. In this case, the trial judge found that a component manufacturer owed no duty of care where it supplied a component and where it was explicitly contemplated in a contract that the manufacturer's materials would be inspected before use. The trial judge found that an inspection was reasonably anticipated in this case and that it would have disclosed defects in the product had it been conducted diligently. The Court of Appeal upheld the decision of the trial judge.

Even where there is no explicit provision for intermediate examination of a manufacturer's product, the manufacturer may still be absolved of its duty of care where an intermediate inspection is expected as of near certainty. In McCain Foods Ltd. v. Grand Falls Industries Ltd., 44 the trial judge found that inadequate and defective welding of a bearing ring during manufacture caused a crane's initial fatigue that led to its ultimate collapse damaging the plaintiff's equipment. The crane's manufacturer had issued 2 service bulletins regarding fatigue of the crane's welded structures, neither of which the defendant received. The trial judge held the defendant fully liable but entitled to full indemnity from the manufacturer. Distinguishing this decision and referring to Donoghue, the Court of Appeal held that there was a reasonable probability that the defects would be discovered before use by an examination that the manufacturer could reasonably have expected to occur hence, providing the manufacturer in this case with an avenue to escape liability in part. 45 The Court asserted that the defendant should have conducted examinations that would have disclosed the faulty welding and moreover, that routine visual inspections were not sufficient. Ultimately, the court apportioned liability between the defendant and manufacturer.

(d) Effect of Intermediate Examination Defence

Comparing the results in Viridian and McCain Foods illuminates the uncertainty regarding the effect of intermediate examination on liability. There remains tension as to whether intermediate examination defences should go to the apportionment of liability or to the removal of the duty of care of the manufacturer. Theall 46 and Edgell 47 warn of the Courts' reluctance to accept an absolute defence based on no duty of care. Rather, they allude to a trend emerging in the jurisprudence suggesting that the result of an intermediate examination defence will most commonly result in a finding of contributory negligence followed by the apportionment of damages.

(e) Conclusion

Central to the issue of intermediate examination is the notion that the probability of an intermediate examination may abrogate a manufacturer's duty of care. Where a manufacturer reasonably anticipates that an intermediate inspection will occur, the manufacturer owes no duty of care. Where a manufacturer does not reasonably anticipate an intermediate examination, it is under an obligation to ensure that the product is free from defects and it carries full liability should the consumer find such a defect. It follows that where a manufacturer does not reasonably anticipate testing and a situation later arises wherein an intermediary conducts an improper examination, the manufacture owes no duty of care. While the body of case law and literature in the area is unsettled, there is an emerging trend that suggest that intermediate examination goes to apportionment of liability rather than an absolute discharge of the manufacturer's duty of care.

V. Intervening Events

Where a defendant in a product liability action has committed a negligent act, whether it be negligent design, manufacture, or failure to warn, and a third party later commits a second negligent act ("the intervening event") that contributes to the plaintiff's injury, the defendant may seek to avoid incurring liability by arguing that the act of the third party had the effect of breaking the chain of causation. A true intervening event acts as a defence in that it breaks the chain of causation by severing any causal link between the negligence of the original tortfeasor and the damages sustained by the plaintiff. To absolve liability, it must be said that the intervening event was the cause of the plaintiff's injury as opposed to the negligence of the defendant. 48 The success of this argument hinges on the forseeability of the intervening event.

A break in the line of causation … is subject to the qualification that if the intervening act is such that it might reasonably have been foreseen or anticipated as the natural and probable result of the original negligence, then the original negligence will be regarded as the proximate cause of the injury, notwithstanding the intervening act.

Also known as novus actus interveniens, this doctrine at one time constituted a complete defence for the original tortfeasor. However, this is generally no longer the case. 49 Apportionment legislation now permits courts to allocate liability among various tortfeasors according to their respective shares of fault. However, where it was not reasonable for the original tortfeasor to have reasonably foreseen the intervening event the doctrine may still provide a complete defence. 50

(a) The General Principle

The Supreme Court applied the doctrine of novus actus interveniens in Bradford v. Kanellos. 51 In Bradford, a kitchen grill had been negligently cleaned, leaving grease on it. The grease caused a fire and an employee used a fire extinguisher to put out the flames. The extinguisher made a hissing noise which caused a patron of the restaurant to panic and shout that gas was escaping and that the kitchen was about to explode. The plaintiff was injured as a crowd of patrons stampeded out of the restaurant. The issue was whether the restaurant owner was liable for failing to clean the grill, which caused the fire and led to the plaintiff's injuries. The Supreme Court found the owner not liable. The Court held that it was not reasonably foreseeable that negligently allowing grease to accumulate on a grill could lead to the plaintiff's injuries in the manner in which they transpired in this case. In so doing the Court confirmed that reasonable forseeability is the proper test to determine if an intervening event may absolve an original tortfeasor from liability.

(b) Intermediate Examination as an Intervening Event

More recently the defence of intervening events was considered in the product liability context in Viridian Inc. v. Dresser Canada Inc. 52 In this case a manufacturer produced diaphragms and supplied them to an intermediary company. The intermediary company incorporated the diaphragms into gas compressors used in the plaintiff's ammonia plant. It was found that deficiencies in the manufacture of the diaphragms contributed to the failure of the compressors thus leading to the loss of the plaintiff. The deficiencies in the diaphragms were discovered upon inspection by the intermediary company but the company continued to use the diaphragms in the repair of the failed compressors. The compressor failed again, and the plaintiff brought an action in negligence against the manufacturer.

The manufacturer sought to avoid liability by arguing that the conduct of the intermediary company following the discovery of the defect constituted a novus actus interveniens which broke the chain of causation between the manufacturer and the plaintiff. The trial court held, and the court of appeal affirmed, that the manufacturer was not liable to the plaintiff. The court stated that it was reasonable for the manufacturer to assume that the intermediary company would conduct its operations with sufficient competence to ensure that diaphragms would not be used if they were inadequate or defective. 53 The court held that a probability of discovery of the defect by the intermediary company was reasonably foreseeable. Therefore where a manufacturer reasonably anticipates that their product will be inspected and tested for defect, this constitutes an intervening cause which breaks the chain of causation. 54

VI. Novel Scientific Theories And Junk Science

As indicated, proof of causation is a complex issue which is central to every product liability action. Often expert testimony is admitted to determine the issue of causation. As a result of the ever-changing nature of scientific knowledge, science once viewed as controversial is now readily accepted and the scientific basis for the evidence has become well established. Having said that, novel and cutting-edge science is also finding its way into the courtroom more and more often. 55 Where areas of expert testimony are well established and familiar, there is generally less need to be concerned about whether the scientific reasoning and methodology underlying the expert opinion is dependable. 56 However, with the advent of more and more novel scientific theories, which are largely untested and by definition not generally accepted, comes an increased risk that expert witnesses will be presenting worthless or misleading information, commonly referred to as "junk science", to legal decision makers who will be unable to identify it as such and who will defer to the 'expert' because of the expert's credentials. 57 In R v. Beland, 58 LaForest J. warned about undue weight being given to "evidence cloaked under the mystique of science."

It is clear, therefore, that the courts must find efficient ways to assess the reliability of novel scientific evidence in order to disallow the admission of unreliable and unsubstantiated science. Canadian jurisprudence has been influenced heavily by the United States Supreme Court decision of Daubert v. Merrell Dow Pharmaceutical, Inc.59 The law in Canada has evolved toward a level of acceptability on this issue with the decisions of the Supreme Court of Canada in Mohan and R v. J.J. The criteria set out for the admission of novel scientific expert evidence will aid the judiciary in identifying those areas of novel science that have acquired sufficient reliability so as to base legal decisions on them.

(a) The Daubert Influence

In 1993 the U.S. Supreme Court developed a comprehensive approach to testing the reliability of scientific and technical evidence given by expert witnesses. In Daubert two minor children and their parents sued Merrell Dow Pharmaceutical Inc. alleging that the children's birth defects had been caused by the mother's ingestion of Bendectin during pregnancy. Bendectin is a prescription antinausea drug marketed by Merrell Dow and was alleged to be the drug which caused birth defects in foetuses of mother's who took the drug. The major issue was causation - had the ingestion of Bendectin during pregnancy caused the children's birth defects? The plaintiffs offered testimony from eight experts alleging that Bendectin had caused the defects. Merrell Dow moved for summary judgement on the basis that the plaintiff's expert's method of analysis was not scientific and thus should, as a matter of law, be inadmissible. The District Court granted summary judgement and the U.S. Court of Appeals affirmed stating that expert opinion based on a scientific technique is inadmissible unless the technique is "generally accepted" as reliable in the relevant scientific community.

The U.S. Supreme Court in Daubert rejected the notion that the test to show that evidence offered by scientists was sufficiently reliable to be admissible was "general acceptance within the relevant scientific community." The Court stated that the "Frye Rule" had been superseded by the adoption of the Federal Rules of Evidence. Rule 702 governs expert testimony and provides,

If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise. 60

The Court articulated that the requirement that an expert's testimony pertain to 'scientific knowledge' established a standard of evidentiary reliability. The Court stated that 'scientific' implied a grounding in the methods and procedures of science and that 'knowledge' meant more than subjective belief or unsupported speculation. 61 More fundamentally, the Court stated that in order to qualify as "scientific knowledge," an inference or assertion must be derived from the scientific method.

Therefore, at the outset, the trial judge must determine whether the expert is proposing to testify to scientific knowledge. The Court outlined many factors which bear on this inquiry:

  2. whether the theory or technique can be and has been tested;
  3. whether the theory or technique has been subjected to peer review and publication;
  4. the known or potential rate of error or the existence of standards; and
  5. whether the theory or technique used has been generally accepted within the relevant scientific community.

Thus, in the United States, "general acceptance" is only one of several factors to be considered in evaluating the soundness of novel science. The holding of Daubert is therefore that judges, as a matter of law, must screen the admission of proffered scientific evidence. Judges were now the "gatekeepers" who would allow only reliable science into the courtroom. 62

The case was remanded by the Supreme Court. On remand the court reviewed the record and the plaintiff's evidence was rejected as "junk science" and summary judgement was affirmed for Merrell Dow. Kozinki J. interpreted the U.S. Supreme Court decision as requiring that the party presenting the expert must show that the expert's findings are based upon sound science, which will require some objective, independent validation of the expert's methodology. The expert's bald assertion of validity was no longer to be enough. The 1995 ruling in Daubert on remand has been capitalized upon as a method to "knock-out" the other side's expert and dispose of the case on a summary judgement motion prior to trial. 63

(b) The Canadian Approach - From Mohan to R v. J.J.

Over the past ten years a dramatic growth in the frequency with which expert witnesses have been called upon to give evidence on issues of, for example, causation in the product liability context, has led to a concern in Canada over the admissibility of novel scientific theories. In Mohan Sopinka J. articulated this concern:

There is a danger that expert evidence will be misused and will distort the fact-finding process. Dressed up in scientific language which the jury does not easily understand and submitted through a witness of impressive antecedents, this evidence is apt to be accepted by the jury as being virtually infallible and as having more weight than it deserves. 64

The seminal Canadian authorities on the admissibility of expert scientific evidence are the decisions of the Supreme Court of Canada in R v. Mohan and R v. J.J. In Mohanthe court stated that before an expert opinion could be admitted into evidence the court had to be satisfied of four things. First the opinion must be relevant to the issues raised in the case. Second, the opinion must be necessary to assist the court to resolve those issues as the information provided by the opinion was beyond the courts experience and knowledge. Third, the opinion must not be excluded by any evidentiary rule and fourth, the proposed witness was properly qualified to give the opinion.

According to Mohan, expert evidence which advances a "novel" scientific theory or technique is subjected to "special scrutiny" to determine whether it meets a basic threshold of reliability. The closer the evidence approaches an opinion on an ultimate issue, the stricter the application of this principle. 65 Therefore, given that in product liability actions scientific expert evidence frequently is determinative of an ultimate issue, namely causation, proffered novel scientific evidence will be subject to a very strict application of the special scrutiny principle. Although the Court in Mohan did not directly mention Daubert or the Daubert criteria, in R v. J.J.the SCC expressly accepted the criteria from Daubertwith the result that "general acceptance" is but one of several factors to be considered in determining whether evidence of a novel scientific theory or technique is to be admitted. In the result, a case-by-case evaluation of novel science is required in order to determine the changing nature of our scientific knowledge. 66 The court in R v. J.J. also stated that in the course of Mohan and other judgements Canadian Courts have emphasized that the trial judge should take seriously their role as "gatekeeper" so as to preclude the admission of junk science into the courtroom. With the decisions in Mohan and R v. J.J. the test in Canada for the admissibility of expert testimony based on novel scientific theory is in line with that of the United States. 67

(i) The Application of "Special Scrutiny"

An examination of the case law shows that as gatekeepers, Canadian judges are applying special scrutiny to determine the admissibility of expert testimony based on novel scientific theory or technique. As indicated, novel scientific theory must be subjected to special scrutiny to determine whether the evidence meets the requisite degree of reliability. In Canada, novel evidence is usually subjected to special scrutiny by way of a voir dire which can occur either immediately prior to trial or during trial. On a voir dire, an expert will give his evidence and be subjected to cross-examination on the reliability of that evidence. The trial judge then determines whether the expert evidence will be admitted by examining whether the testimony meets the necessary indicia of reliability.

Grant v. Dube 68 was a motor vehicle case in which damages were at issue. At trial the plaintiff proposed to call an expert in psychology to give evidence that the source of the plaintiff's pain was physical. The defence challenged the evidence as "junk" arguing that the conclusion relied upon measurements of electromyographic (EMG) activity, and that the use of EMG measurements as a basis for reaching conclusions as to the cause or source of pain was novel scientific evidence. Although the case does not outline the procedure followed after the defendant's objection, it appears that a voir dire was held to determine the admissibility of the plaintiff expert evidence. On the voir dire evidence was given by both sides with regard to the acceptance of EMG in the scientific community. In refusing to admit the plaintiff's expert report, the court held that where a party seeks to adduce novel scientific evidence and an objection to it is made, the law requires the person seeking to introduce the evidence to prove its admissibility. The court referred to the case of U.S.A. v. Jakobetz, 69 for factors for consideration in assessing the reliability of novel scientific evidence. The fourteen factors listed in this case are factors which were later considered in Daubert.

In Wolfin v. Shaw70 it was determined that the use of a positron emission tomography (PET) scan for diagnostic determination of mild traumatic brain injury was novel science and thus should be subjected to special scrutiny in order to determine reliability. On the voir dire the judge explicitly referred to the Daubert criteria and stated that such have found their way into Canadian jurisprudence. 71 The Daubert criteria influenced the decision of the judge to exclude the testimony of the plaintiff's witness. It was held that there was not a substantial body of literature accepting the use of PET for diagnosis of brain injury. In addition, the plaintiff expert had not published a peer reviewed article on the use of PET which he was proposing. The court also held that the fact that the scan had not been requested by the plaintiff's treating physician nor requested prior to the commencement of the litigation raised concerns with respect to its scientific validity.

More recently in Italy v. Seifert72 quantitative electroencephalograph (QEEG) test results were sought to be admitted into evidence in order to show that Seifert was mentally fit to conduct his extradition hearing. The Republic of Italy challenged the evidence as novel science and sought to have it excluded on the basis it constituted "junk". The QEEG results were held to be novel science and thus subject to special scrutiny by the trial judge to determine their reliability. The court noted the gatekeeper function of the trial judge and excluded the QEEG evidence on the basis that the results did not meet the requirements needed to admit evidence based on novel science. 73 In so holding the court applied the four factors that were referred to in Daubert and adopted by the SCC in R v. J.J. Those factors include: whether the theory can be or has been tested, whether the theory has been subjected to peer review and publication, whether the potential rate of error is known, and whether the theory used has been generally accepted. 74

(ii) The Procedure of Daubert

Despite our adoption of the Daubert criteria and the notion that judges must act as gatekeepers to the admission of unsubstantiated science into the court, in Canada there is no means to challenge expert evidence on a summary judgement motion prior to trial as is the case in the United States. The use of Daubert hearings is blocked in Ontario by a procedural anachronism. 75 Specifically, discovery of expert witnesses is unavailable. Therefore the only explanation of the reasoning and methodology which forms the basis of the expert's conclusions are those included in the expert report. The Ontario Rules of Practice do not compel experts to spell out their reasoning and methodology in their reports. Rule 53.03 reads as follows:

A party who intends to call an expert witness at trial shall … serve a report … "signed by the expert, setting out his or her name, address and qualifications and the substance of his or her proposed testimony."

Expert reports are therefore often deliberately ambiguous. The result is that it is not until the expert has been qualified to give evidence, and in fact gives evidence at trial, that the basis for his evidence becomes apparent. By that time his evidence has been admitted and any attack on his evidence is all too often regarded as going to weight, not admissibility. 76

More problematic, given this state of the law in Ontario, our system tolerates unreliable expert evidence prior to trial. Because there is no means by which to discover the reasoning behind an experts conclusions, ambiguous and misleading expert reports continually are relied upon in pre-trials or non judicial settlement arrangements where testing of the expert on a voir dire by way of cross examination is not available. 77 The result is that defendants, for example manufacturers of products who defend product liability claims, are funding the costs of litigation and paying judgments based on unreliable expert evidence. 78

(iii) Possible Solutions

Some have argued that the answer is to adopt a summary judgment procedure akin to a Daubert hearing whereby the reliability of expert evidence could be challenged prior to trial. To facilitate this, amendments to the Rules of Civil Procedure would be needed. In particular, Rule 53.03 would need to be amended so as to compel an expert to outline in his report a detailed account of the reasoning and methodology relied upon to reach his conclusions and/or the Rules would need to be amended to allow for the discovery of expert witnesses. Making the expert's reasoning known would allow that reasoning to be challenged as unreliable prior to trial. This would allow claims based on junk science to be eliminated at an earlier stage of the litigation process thus leading to a more efficient allocation of resources - it would save the parties both time and money and would also have the effect of injecting credibility and thus confidence into our judicial system.

However, the argument in favour of a pre-trial motion to challenge the admissibility of the reasoning of an expert witness and dispose of the action by way of summary judgment ignores Canadian substantive law. For instance, the interpretation the Supreme Court has given to causation in Snell and Athey would probably prevent a court from disposing of an action by way of summary judgment on a Daubert application. Snell indicates that a plaintiff need not have positive or scientific proof of causation. In Athey it was indicated that, in appropriate cases, the plaintiff need only show that the defendant's action materially contributed to the plaintiff's injury. This low threshold of proof has been interpreted by some to say that no expert evidence is required to prove causation in a medical malpractice case where there is a definite breach of duty by the defendant and uncertainty as to which particular event triggered the injury. 79 If this interpretation is accepted in the product liability context, it will be extremely difficult to dispose of a case via summary judgment by simply excluding the evidence of an expert whose testimony speaks to causation. This problem is exacerbated by the fact that on a motion for summary judgment the court is loath to have an action disposed of via summary judgement - it will only be the most obvious of cases, where there is no "genuine issue for trial", where summary judgement is granted. The more appropriate approach to Daubert is to use the procedure to block the admissibility of evidence of a specific expert witness. In other words, it need not be used to support an application for summary judgement but could be used simply to eliminate the evidence of a particular witness. 80

In addition, it would appear that adding a Daubert procedure would simply lengthen the trial and unnecessarily complicate the process. In many cases, as much time would be consumed in a pre-trial application as would be taken at trial. 81 Moreover, there is a risk that if the Daubert hearing is heard by the judge where the Daubert hearing does not succeed, and the evidence is admitted that the evidence is enhanced as more reliable.

There has been some discussion about the possibility for a legislated solution. However, lobbying government to change or modify the law of civil procedure requires an interest group committed to change and in Canada no such group has appeared. In the United States it was the manufacturers of products who were continually defending product liability actions which pressured for a change in how expert evidence was handled. To date there appears to be no pressure from institutional defendants in Canada. 82

Perhaps the solution is much more fundamental. Because there is no reason to think that the community of experts, will on their own volition, make any efforts to increase the reliability of expert testimony, the legal community should take it upon themselves to ensure that "junk" science does not enter the courtroom. The best way to accomplish this is to be aware of the problem and more importantly, be aware of the fact that where novel science is proffered, that its admissibility is no longer automatic. As discussed, there is a growing body of case law whereby expert testimony based on novel science can be challenged and is being excluded from admission due to a lack of reliability. However, it is counsel who decide whether and to what degree to cross-examine the intellectual underpinnings of the proposed expert evidence. If there is no principled objection by counsel to the admission of the proposed expert evidence and the witness is qualified, a witness may give an astonishing range of evidence. Whether the trial judge accepts the evidence is not the issue - once the evidence is in the record there is material for the Court of Appeal to reverse the trial judge. 83 Being aware of the procedures available will go a long way to prevent the admission of junk science into our courtrooms.

VII. Conclusion

In the product liability context it is clear that developments in both the law of causation and the law regarding the admissibility of novel scientific theory are of particular interest. Where the admissibility of novel scientific theory is brought into issue, judges are applying special scrutiny to ensure that only evidence which meets the necessary indicia of reliability is admitted. In so doing, Canadian judges are living up to their role of gatekeeper. In the future, courts should be encouraged to apply the special scrutiny principle in a firm and meaningful fashion with respect to views that have yet to receive general acceptance, before a trier of fact is asked to apply those views to determine the outcome of litigation. The problem lies in the fact that the admissibility of novel science is not brought into issue frequently enough. Canadian substantive law has evolved to the point where the indicia to measure reliability are sufficient to exclude evidence which is not reliable enough to base legal decisions upon. Counsel need to take advantage of the precedents which exist in order to ensure that Canadian courts remain free of junk science.


1Mark Skorak, "Admissibility of Expert Evidence" (Personal Injury Conference - Continuing Legal Education Society of British Columbia, 7 February 2003) [unpublished], [hereinafter Skorak] at 8.

2David Paciocco et al., The Law of Evidence: 3rd ed. (Toronto: Irwin Law, 2002), [hereinafter Paciocco] at 172.

3[1994] 2 S.C.R. 9 [hereinafter Mohan].

4[2000] 2 S.C.R. 600 [hereinafter R v.J.J. ].

5Lewis N. Klar, Tort Law, 3rd ed. (Toronto: Thomson Limited, 2003), [hereinafter Klar] at 388.

6[1990] 2 S.C.R. 311 [hereinafter Snell].

7Ibid., at 326.

8Klar, supra note 5 at 389.

9Lawrence Theall, Product Liability, Loose-leaf (Aurora: Canada Law Book, 2001) [hereinafter Theall] at L7 - 10.

10Snell, supranote 6 at 319 - 320.

11[1952] 2 All E.R. 402.

12Ibid. at 402.

13Snell, supra note 6 at para 15.


15Theall, supra note 9 at L7 - 6.

16Snell, supra note 6 at para 26.

17One such alternative was advocated in McGhee v. National Coal Board, [1973] 1 W.L.R. 1 (H.L.) whereby Lord Wilberforce stated that the plaintiff need only prove that the defendant created a risk of harm and that the injury occurred within the area of the risk. Moreover, comments by the court in Walker Estate v. York-Finch General Hospital (2001), 198 D.L.R. (4th) 193 (S.C.C.) suggest that at least two alternative theories of causation may be applied in particular scenarios. The two tests are the presumptive link test and the material contribution test.

18Theall, supra note 9 at L7 - 6.

19[1996] 3 S.C.R. 458 [hereinafter Athey].

20Ibid. at para 16.

21[2001] 1 S.C.R. 647 [hereinafter Walker Estate].

22[2003] A.J. No. 685.

23Ibid. at para 54.

24Robert Black, "Duty to warn and Products Recall" (Canadian Litigation Counsel Products Liability Seminar, King Edward Hotel, Toronto, September 2000) [unpublished] [hereinafter Black] at 4.

25[1972], S.C.R. 569 [hereinafter Lambert].

26Ibid. at 574 -575.

2754 O.R. (2d) 92 [hereinafter Buchan].

28 [1995] 4 S.C.R. 634 [hereinafter Hollis].

29Ibid. at 653.

30Ibid. at 653 - 654.

31 [1974] S.C.R. 1189.

32Ibid. at 1200.

33Theall, supra note 9 at L7 - 10.

34 [1980] 2 S.C.R. 880.

35Dean Edgell, Product Liability in Canada, (Toronto: Butterworths, 2000) [hereinafter Edgell] at 79.

36Buchan, supra note 27.

37Hollis, supra note 28 at 675 - 676.

38Theall, supra note 9 at L7 - 12.

39 [1932] A.C. 562 (H.L.) at 599.

40 [1938] 4 All E.R. 803 (K.B.)

41Theall, supra note 9 at L7-18.1.

42 [1944] O.R. 207.

43 (2000), 274 A.R. 28 at p.88 (Q.B.), aff'd 216 D.L.R. (4th) 122 (C.A.) [hereinafter Viridian].

44 (1990), 67 D.L.R. (4th) 29 (N.B.Q.B.), rev'd 80 D.L.R. 4th 252, leave to appeal to S.C.C. refused 85 D.L.R. (4th).

45Theall, supra note 9 at L7-18.

46Ibid. at L7-19.

47Edgell, supra note 35 at 89.

48Ibid. at 83.

49A.M. Linden, Canadian Tort Law 6th ed. (Toronto: Butterworths, 1997) at 460.


51 [1974] 1 S.C.R. 409.

52Viridian, supra note 43.

53Ibid. at para 372.

54Theall, supra note 9 at L7 - 24.

55Expert evidence will constitute novel science where the scientific theory relied on has not yet been generally accepted in the relevant field of endeavour, or where the particular use made of a generally accepted theory or technique has not yet been generally accepted in that field.

56Paciocco, supra note 2 at 172.


58 [1987] 2 S.C.R. 398.

59509 U.S. 579 (1993) [hereinafter Daubert].

60Ibid. at 12.


62David Eyou, "Why Isn't Daubert Being Used in Ontario Civil Cases?" (Eryou Barristers, Thunder Bay, 26 January 2000) [hereinafter Eryou] at 9.

63Ibid. at 9 - 10.

64Mohan, supra note 3 at para 19.

65Ibid. at para 28.

66Skorak, supra note 1 at 4.

67See, for example, the comments of R.J. Delisle in "The Admissibility of Expert Evidence: A New Caution Based on General Principles", 29 C.R. (4th) 267 at 272 where it is suggested that the position in Mohan is the same as Daubert. "Trial judges will be … expected to assess whether the reasoning or methodology underlying the testimony is scientifically valid and whether or not the reasoning can properly be applied to the facts."

68 (1992), 12 C.P.C. (3d) 22.

69747 F.Supp 250 (1990).

70 [1998] B.C.J. No. 5.

71Ibid. at para 19.

72 [2003] B.C.J. No. 726.

73Ibid. at para 110.

74Ibid. at para 102.

75Eryou, supra note 62 at 23.

76Ibid. at 23 - 24.

77Ibid. at 8.

78Ibid. at 9.

79Eryou, supra note 62 at 45.

80See, for example, the discussion in Eryou, supra note 62 at 35 - 39.

81These were the arguments advanced in the United States against the establishment and expansion of the development of Daubert applications.

82Eryou, supra note 62 at 45.

83See, for example, Kenny v. Waterloo County Board of Education (1999), 45 O.R. (3d) 1 (C.A.) as cited in Eryou.


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