2018 Causation Update

by Simon Clements | Oct 18, 2018

In 2018, the test to establish causation is clear. What remains unclear is how that test is to be translated into jury questions, and how the Court will assess the evidence to determine if a plaintiff has met that test.  This paper will consider those current issues.

The Test

Care must also be taken to separate the articulation of the test, from the Courts’ commentary on how the evidence is to be assessed in order for a plaintiff to meet the onus of proof and establish causation. “Robust and pragmatic” is an approach to the analysis of evidence.  Robust and pragmatic is not a test.

As currently formulated by the Supreme Court in Clements v. Clements [2012] 2 S.C.R 181:

The test for showing causation is the “but for” test.  The plaintiff must show on a balance of probabilities that “but for” the defendant’s negligent act, the injury would not have occurred.  Inherent in the phrase “but for” is the requirement that the defendant’s negligence was necessary to bring about the injury – in other words that the injury would not have occurred without the defendant’s negligence. 

(emphasis in original) (Clements at para. 8)

In all of the Supreme Court’s jurisprudence where it has returned to the causation test, Clements is the first time the court has inserted the word necessary in a description of the test.  As a result, lower courts and counsel must now consider the meaning of necessary and the impact this additional word has on the “but for” causation analysis.

How Did We Get Here?

In Snell v. Farrell [1990] 2 S.C.R 311, the Supreme Court dealt with a medical malpractice action where the question was whether the plaintiff’s eye injury was caused by the negligence of the defendant eye surgeon during a cataract removal procedure, or whether the loss of vision was due to the plaintiff’s high blood pressure or diabetes which could also have caused pressure to be exerted on the optic nerve, cutting off the blood supply and causing the plaintiff’s loss of vision.  At trial, neither expert was able to express with certainty an opinion as to what caused the injury to the optic nerve or when it occurred. Before turning to alternative formulations of the causation test, Justice Sopinka at pages 319-320 stated that the traditional causation principle is that “the plaintiff must prove on a balance of probabilities that, but for the tortious conduct of the defendant, the plaintiff would not have sustained the injury complained of.” This then is the traditional formulation of the “but for” test.  Separate from the statement of the test is Justice Sopinka’s treatment of how the elements is to be analyzed.  That is where the oft-cited expression “robust and pragmatic approach to the facts” comes from.  At page 330:

The legal or ultimate burden remains with the plaintiff, but in the absence of evidence to the contrary adduced by the defendant, an inference of causation may be drawn although positive or scientific proof of causation has not been adduced.  

Where there is some evidence of different theories of causation, then the court is to consider all of that evidence and take a robust and pragmatic approach to the facts in drawing an inference.  Having assessed the evidence, the trial judge is then permitted to draw inferences.  The tricky issue is to identify an appropriate inference versus an inappropriate speculation.  On this issue, at page 336, Justice Sopinka stated “it is not speculation but the application of common sense to draw such an inference where, as here, the circumstances, other than a positive medical opinion, permit”.

In 1996, the Supreme Court’s decision in Athey v.Leonati [1996] 3 S.C.R 458 caused 10 years of confusion because it appeared to condone the use of an alternate test, the “material contribution” test.

Mr. Athey was a person with a history of back problems.  He suffered back and neck injuries in an MVA. While still recovering from those injuries, he suffered a further injury in a second MVA.  Six months later, his doctor cleared him to return to his regular exercise routine.  While warming up, he suffered a herniated disc.  The issue at trial was the cause of the disc herniation and whether it was caused by the injuries sustained in the two MVAs or whether it was attributable to his pre-existing other back problems.  The trial proceeded against the drivers in the two MVAs.  Both drivers admitted liability.  The trial was fought on causation.  The trial judge determined that the two car accidents played “some causative role” in the overall outcome and fixed that percentage at 25%.  Since she held that since the accidents were a 25% cause of the disc herniation, she awarded 25% of the damages which had been assessed.  Mr. Athey’s appeal to the Court of Appeal was that he was entitled to 100% of the damages, given the finding that the injuries sustained in the MVAs were a cause of the disc herniation on the basis that a “material contribution” to the injury should be sufficient to achieve 100% recovery.  As this argument was not raised at trial, the Court of Appeal would not consider it and dismissed the appeal.

The Supreme Court allowed the appeal and awarded 100% of the damages which had been assessed. Justice Major started at paragraph 13 by stating, “causation is established where the plaintiff proves to a civil standard on a balance of probabilities that the defendant caused or contributed to the injury”, citing Snell. While no pin point citation was given in the judgment, it appears that Justice Major took the “caused or contributed” language from this wording in Snell at page 326:

Causation is an expression of the relationship that must be found to exist between the tortiousact of the wrongdoer and the injury to the victim in order to justify compensation of the latter out of the pocket of the former.  Is the requirement that the plaintiff prove that the defendant’s tortious conduct caused or contributed to the plaintiff’s injury too onerous? 

(emphasis added)

It should be noted that “caused or contributed” is not part of the traditional formulation of causation referred to above that the “plaintiff must prove on a balance of probabilities that but for the tortious conduct of the defendant, the plaintiff would not have sustained the injury complained of”. Justice Major’s concept of contribution to the injury, as part of the formulation of the test, was new.

Justice Major proceeded to note that the “but for test is unworkable in some circumstances” so the courts have recognized that causation is established where the defendant’s negligence “materially contributed” to the occurrence of the injury… A contributing factor is material if it falls outside the de minimisrange” (at para. 15).  When material contribution can be used to establish causation was not explained and, therefore, it appeared to establish an alternate causation test in multi-tortfeasor cases. At paragraph 17, Justice Major stated:

As long as a defendant is part of the cause of an injury, the defendant is liable, even though his act alone was not enough to create the injury. There is no basis for a reduction of liability because of the existence of other pre-conditions: defendants remain liable for all injuries caused or contributed to by their negligence.

(emphasis in original)

As a result, the Supreme Court determined that Mr. Athey was entitled to the full amount of the damages which had been assessed.

In 2007, the Chief Justice determined the time had come to “right the ship” and reassert that the test for causation is “but for” and not “material contribution”.  In Resurfice Corp. v. Hanke [2007] 1 S.C.R 333, the plaintiff placed a water hose into the gasoline tank of an ice resurfacing machine by mistake.  The plaintiff alleged that the water tank and gas tank were similar in appearance and had been placed close together so this design defect made it easy to confuse the two tanks.  The plaintiff turned on the hot water hose and the water which poured into the gasoline tank vaporized the gasoline which was released into the air.  Heat from an overhead heater caused the vapor to ignite, causing an explosion in which the plaintiff was badly burned.  He sued the manufacturer and distributor of the ice resurfacing machine for design defects.

The plaintiff lost at trial.  The trial judge held that the plaintiff failed to establish both legal and factual causation.  First, the judge held that it was not reasonably foreseeable that this mistake would have been made. Therefore, the injury was too remote to be compensated. Second, the trial judge held that the accident was caused by the plaintiff’s own decision to turn the hose on when he ought to have known the hose was in the wrong tank. The Court of Appeal overturned the decision, finding palpable and overriding errors in the foreseeability analysis and stated that the trial judge should have used the material contribution test rather than the but for test in determining factual causation.

The Supreme Court restored the trial decision.  The Chief Justice stated that there were no errors in the foreseeability analysis.  Therefore, the damages were remote.  The decision could have stopped there but the Chief Justice determined that it was necessary to address the confusion over the use of the material contribution test.  At paragraph 21, the Chief Justice stated:

The basic test for determining causation remains the “but for” test.  This applies to multi-cause injuries.  The plaintiff bears the burden of showing that “but for” the negligent act or omission of each defendant, the injury would not have occurred. 

Thereafter, the Chief Justice set out the limited circumstances under which the material contribution exception could be used.

This was very clear.  The Chief Justice determined that “but for” needed to be explained further is not evident, but that is what she did in 2012 in Clements v. Clements [2012] 2 SCR 181.

Clements is an MVA case.  Mr. Clements was driving a motorcycle with Mrs. Clements on the back. The motorcycle was 100 pounds overloaded with weight.  Unbeknownst to Mr. Clements, a nail had punctured the rear tire.  At a time in which Mr. Clements was driving 120 km/h in a 100 km/h zone, the nail fell out, the tire deflated and he lost control of the motorcycle.  Mrs. Clements was thrown off the back and sustained a traumatic head injury.  At trial, it was conceded that Mr. Clements was negligent in driving an overloaded bike too fast.  The issue at trial was what caused the accident.  An accident reconstruction expert who testified for the defendant stated that the cause of the accident was the tire puncture and deflation and the accident would have occurred without the negligence of Mr. Clements.  The trial judge found that Mrs. Clements, through no fault of her own, was unable to prove “but for” causation due to the limitations of scientific reconstruction evidence. The trial judge applied a material contribution test instead and found Mr. Clements liable on this basis.  The Court of Appeal set aside the judgment and dismissed the action on the basis that “but for” causation had not been proved and the material contribution test did not apply.

In the Supreme Court, the Chief Justice, writing for the majority, picked up where she had left off in Resurface and stated at paragraph 8:

The test for showing causation is the “but for” test.  The plaintiff must show on the balance of probabilities that “but for” the defendant’s negligent act, the injury would not have occurred. Inherent in the phrase “but for” is the requirement that the defendant’s negligence was necessary to bring about the injury – in other words that the injury would not have occurred without the defendant’s negligence.  This is a factual inquiry.  If the plaintiff does not establish this on the balance of probabilities, having regard to all the evidence, her action against the defendant fails. 

In retrospect, it has proved to be unhelpful that the Chief Justice considered that an explanation of “but for” was needed.  As we will see in the cases dealing with how “but for” is to be explained to the jury, some judges believe the addition of “necessary” is confusing because in multi-tortfeasor cases it must be read in the context of the plaintiff needing only prove the individual defendant was a cause of the injury to succeed.  That cause must be a necessary cause. It must also be a contribution that is beyond the de minimis range.  Having determined that the wrong test was used at trial, the majority of the Supreme Court sent the case back to the trial judge for a new trial using the “but for” test.  The minority would have dismissed the action on the basis that the evidence available at trial was considered by the trial judge and did not meet the “but for” test.

While not necessary to do so in the result, the Supreme Court dealt with for the first time since Snell v. Farrell with how the evidence is to be assessed when applying the “but for” test to the evidence.  The Chief Justice stated at paragraph 9:

The “but for” causation test must be applied in a robust common sense fashion. There is no need for scientific evidence of the precise contribution the defendant’s negligence made to the injury. 

Finally, in 2013, in the medical malpractice case of Ediger v. Johnston [2013] 2 S.C.R 1998, the Supreme Court reiterated the test taken from Clements paragraph 8 as follows:

This Court recently summarized the legal test for causation in Clements v. Clements. Causation is assessed using the “but for” test. That is, the plaintiff must show on a balance of probabilities that “but for” the defendant’s negligent act, the injury would not have occurred. 

(citations removed)

The Court went on to reiterate that the negligence must be “necessary” to bring about the injury.

On the application of the test, the Court restated the approach to the evidence from Snell. The Court stated at paragraph 36:

The trier of fact may, upon weighing the evidence, draw an inference against a defendant who does not introduce sufficient evidence contrary to that which supports the plaintiff’s theory of causation. In determining whether the defendant has introduced sufficient evidence, the trier of fact should take into account the relative position of each party to adduce evidence. 

Application of These Principles by the Ontario Court of Appeal

The Ontario Court of Appeal has not formulated any alternative causation test.  It has accepted the formulation, from time to time, as articulated by the Supreme Court. Where the Court of Appeal has been inconsistent is in its approach as to what evidence is required for a plaintiff to satisfy the onus of proof.

As stated originally in Athey v. Leonati, and reiterated in Clements, scientific precision is not required to satisfy the causation element of negligence.  Clements reaffirmed that there is no need for scientific evidence of the precise contribution the defendant’s negligence made to the injury (Clements at paragraph 9).  The question then becomes what evidence is required for a plaintiff to meet the burden of proof.  Snell v. Farrell stated that in the absence of evidence to the contrary, causation could be inferred.

The Ontario Court of Appeal has been inconsistent in its treatment of the inference-finding powers of the trial judge.  There remains a question as to what inferences a trial judge can make using her own common sense versus the requirement that a properly qualified expert testify about the inferences to be drawn from the facts at which point it would be appropriate for the trial judge to accept or reject that opinion.

In Goodwin v. Viljoen (2012) ONCA 896, both Justice Feldman, for the majority, and Justice Doherty, in dissent, described the limits of the trial judge’s inference drawing power.  At paragraphs 124 and 134 of the Decision, Justice Feldman stated that it was the job of the expert to fill in the scientific gaps. The expert by virtue of his or her training and experience is in the best position to make an educated guess as to what the likely outcome would have been “but for” the negligence.  This, it is submitted, is consistent with the dictum that causation need not be proved with scientific precision.  If the expert is able to make an educated guess, that is sufficient to meet the evidentiary burden.  As stated by Justice Feldman at paragraph 134, the trial judge must not step in and act as her own expert.  Therefore, there is a limit on how far the trial judge can go in drawing inferences. Justice Feldman thought that the trial judge had not crossed the line in this case.  Justice Doherty disagreed and stated that the finding of the trial judge merely amounted to speculation, even when based on permissible common sense inference drawing was not sufficient to meet the burden of proving causation.

It is submitted that this analysis by the Court is correct. When thinking about the first principles of calling expert evidence, the judge, as gatekeeper, must consider whether the proposed evidence of the expert is necessary by being outside the knowledge and experience of the trier of fact.  If the expert is qualified as having that unique knowledge base which is going to be helpful to the fact finding process, then the trial judge has explicitly acknowledged that she does not have the basis for drawing inferences from a set of scientific facts. Therefore, what should be done, it is submitted, is have the expert fill in the gaps and for the trial judge (or jury) to accept or reject the inferences drawn by the expert.

However, this argument was made by the appellants in Ghassi v. Singh 2018 ONCA 764 and was rejected.  In that case, even though the expert witness offered to provide an educated guess and plaintiff’s counsel asked him not to, the result being that there was no expert evidence on the critical causation point of whether treatment at a certain time would have been effective, the Court of Appeal held that there was sufficient other evidence upon which the trial judge could base a reasonable inference.

Unfortunately, it is impossible to say in any given case which way the Court of Appeal will go on the inference drawing issue. There is a line between inference drawing and acting as your own expert.  Where the Court of Appeal will draw that line in any given case is unknown and makes the outcome of causation appeals very difficult to predict

The Formulation of Jury Questions

As has already been pointed out in papers authored by Maria Damiano and David Chaifetz, there is an inconsistency in the Court of Appeal’s formulation of jury questions in multiple tortfeasor medical malpractice cases which have followed Clements.

In Surujdeo v. Melady 2017 ONCA 41, the patient, Ms. Surujedo was brought to the hospital by ambulance for cardiac care and treatment.  The trial proceeded against the defendant emergency physician Dr. Melady and defendant respirologist, Dr. Soicher.  Approximately 10 hours after arriving at the hospital, Ms. Surujedo died.  An autopsy revealed that she died of myocarditis, an inflammation of heart muscle caused by a viral illness. When Dr. Melady first assessed Ms. Surujedo in the emergency department, he diagnosed her with viral pericarditis, an inflation of the sac around the heart caused by a viral infection.  In retrospect, this was a wrong diagnosis.  The issues at trial related to the review of test results which may have ruled out pericarditis earlier and which may have afforded a chance of recovery if the myocarditis had been treated.  The causation issue at trial concerned whether there was anything the physicians could reasonably have done to avoid Ms. Surujedo’s death given the aggressive form of her viral myocarditis, the short amount of time in which to diagnose and treat her condition and the lack of certain required treatment at the hospital. (Court of Appeal at para. 4)

An issue arose at trial as to the wording that the trial judge (Justice Gans) would provide to the jury in the jury questions.  The trial judge approved two jury questions for each physician.  The first asked whether that physician had breached the standard of care. If the jury concluded that the physician had, the second question went on to ask:

Has the plaintiff established on a balance of probabilities that this physician’s breach of the standard of care was a cause of Rossana Surujedo’s death?

(emphasis added)

At trial, the physicians objected to that form of question. They argued that “but for” was the appropriate causation test and that the inclusion of the words “a cause” was not consistent with “but for” causation.

The Court of Appeal (at paragraph 93) ruled that “the trial judge erred in law by approving jury questions that did not reflect the applicable “but for” causation test”.  Justice Brown went on to approve the formulation of a jury question by Justice Darla Wilson in Sacks v. Ross 2015 ONSC 7238 stating that he adopted the following analysis by Justice Wilson:

There is no compelling reason not to use the language of causation from Clements and other cases when drafting the questions for the jury on causation. The legal test is articulated by the Supreme Court of Canada is clear: but for the defendant’s negligent act, the injury would not have happened.

I will instruct the jury on the law as it relates to causation and will use the “but for” test.  I see no advantage to departing from the legal test as articulated by the Supreme Court of Canada when asking the jury to answer the questions on causation. 

The answers on causation will read as follows:

If your answer to question #1(a) is YES, have the plaintiffs proved on a balance of probabilities, that but for the breach of the standard of care, the injuries of Jordan Sacks would not have occurred? 

Therefore, what the Court of Appeal said in Surujdeo is that any formulation of the causation question for the jury which involves the jury considering a contribution to the injury, harkening back to the “caused or contributed to” language, is legally wrong.  The correct formulation of the causation question is “but for”. The question proposed by Justice Gans, which was whether the breach was “a cause” was not consistent with “but for”.  “A cause” means something that is contributory.

Sacks v. Ross 2017 ONCA 773 also went to the Court of Appeal, also on the formulation of the jury questions. The Surujedo decision was released on January 18, 2017. The Sacks appeal was heard on May 17, 2017.  There is no doubt that the Sacks panel knew the decision of the Surujedo panel.  In fact, Sacks cites Surujedo on another point.  However, when it came to the formulation of the jury questions, in Sacks the appellants asserted that phrasing the jury questions in terms of the language of the “but for” test as set out in Clements, would confuse the jurors, particularly in using the word “necessary”, which suggests that each defendant’s conduct must be the sole cause of the plaintiff’s injury.  They pointed out that in delayed diagnosis cases, one defendant’s conduct will rarely, if ever, be the sole cause (Sacks appeal at paragraph 68).  The appellants asked for a jury question as follows:

Did the failure of             to meet the standard of care cause or contribute to Mr. Sacks’ injury?

The respondents, on appeal, being the physicians, nurses and hospital, had argued at trial that the correct formulation should be the Clements wording per  D. Wilson J. in Sacks that was approved and was then endorsed by the Court of Appeal in Surujedo.  This was completely ignored by the Sacks panel.  Justice Lauwers proposed a new set of jury questions as follows:

  1. Have the plaintiffs proven, on a balance of probabilities, that a delay in treatment caused Jordan Sacks’ injuries?

If the answer to that question is “yes”, in respect of each individual defendant: 

  1. Have the plaintiffs proven, on a balance of probabilities, that the delay resulting from [this defendant’s] breach of the standard of care caused or contributed to the injuries of Jordan Sacks?

If the answer to that question is “yes”, in respect of each individual defendant:

  1. How did [this defendant] breach the standard of care?

Please provide clear and specific answers.

The first observation is the direct conflict between the Surujedo panel which endorsed a jury question that specifically eliminated “caused or contributed to” being put to the jury versus question #2 by the Sacks panel which asks whether the breach “caused or contributed to the injuries”.

The second observation revolves around the issue of the word “necessary”.  As already stated, the Chief Justice explained the “but for” test in Clements as meaning that the involvement of the defendant in question was “necessary” to bring about the result.  Justice Lauwers stated at paragraph 18:

As I interpret Clements, in specifying the “but for” test, McLachlin C.J. used the word “necessary” in a purposive manner in order to underscore the legal requirement for the plaintiff to prove that there was a real and substantial connection between the defendant’s breach of the standard of care by an act or omission and the plaintiff’s injury.

(emphasis added)

It was Justice Lauwers’ view that using the word necessary was not appropriate and it, alone, may have the result of confusing the jury.  As David Chaifetz has noted while Justice Lauwers’ has attempted to eliminate one source of confusion by eliminating the use of the word necessary, he has added another source of confusion by introducing the concept that there be “a real and substantial connection” between the defendant’s breach of the standard of care and the plaintiff’s injury.  Nowhere in any of the Supreme Court decisions is the term “real and substantial connection used”.  Recall in this context that for an act to be causative, the contribution of that act to the result must be beyond the de minimis range. The de minimis criteria was introduced in Athey v. Leonati, but has never been defined.  In Athey, the prior MVAs were found to be at least a 25% contribution to the disc herniation and that was found to be beyond the de minimum range.  Therefore, de minimis means something less than 25% but what that something is remains unknown. By referring to the “real and substantial connection”, Justice Lauwers appears to be harkening back to a similar idea that the contribution of the individual defendant must be “real and substantial” in the sense that it is beyond de minimis.  The question then becomes can you have a necessary contribution which is de minimis?  In other words, if the contribution is found to be de minimis, does that mean, by definition, that the contribution was not necessary to bring about the result?

An additional problem with the Sacks formulation of the jury questions is that these jury questions do not actually help the analytical problem of determining whether each of the seven defendants, who were found to have breached the standard of care, were necessary contributors.  The reason for this is that the causation issue, at trial, was actually the simple question of whether the delay in diagnosis led to sepsis which led to the amputations or whether the sepsis was caused by an alternative infection.  The jury chose the alternative infection option and, therefore, never had to consider the individual contribution of each of the potentially liable defendants.  In my submission, the Lauwers’ formulation does not work as it is impossible to go defendant by defendant in a delayed diagnosis case and determine whether the hour here or there caused by the negligence of an individual defendant was a necessary cause of the outcome.

Notwithstanding his finding that the jury questions were incorrectly phrased, Justice Lauwers determined that the outcome would not have been different with correct jury questions because the jury determined that the cause of the injury was the alternative infection.  Mr. Sacks sought leave to appeal to the Supreme Court.  Surprisingly, in the face of inconsistent jury questions in Surujdeo and Sacks, the Supreme Court refused to grant leave.  This may be because the entire discussion of the appropriate form of the jury questions in Sackswas, based on the result, obiter dicta.  Perhaps the Supreme Court determined on that basis that Justice Lauwer’s formulation did not need further analysis.  For an excellent paper on how to approach the causation analysis as mandated by Sacks, please see “Common-Sense Causation: How a Robust and Pragmatic Application of the “But For” Test Can Solve the Circular Causation Problem in Cases of Multiple Contributing Tortfeasors” by Brooke MacKenzie and Alexi Wood.

The Way Forward – Cheung v. Samra

Darla Wilson J. issued an important decision in Cheung v. Samra (2018) ONSC 3480, released on June 5, 2018.  In this case, the issue is whether brain damage to the infant plaintiff occurred in or around the time of her birth or whether it was unrelated to her birth.  At the end of this jury trial, Justice Wilson had to determine the correct form of the jury questions and, without referring to Sacks v. Ross, declined to follow it, stating at paragraph 16:

In oral reasons delivered on April 24, I ruled that the proper language for the causation questions was not “caused or contributed to” but rather the language employed by the Supreme Court in Clements, and other cases, asking whether “but for” the negligence would the plaintiff have sustained the damage. Furthermore, I rejected the use of the threshold question prior to answering the causation questions. 

The threshold question, it will be recalled, is the first question of Justice Lauwer’s asking whether causation has been established without reference to the role that individual defendants played in the sequence of events.  Sacks was directly on point and was binding on Justice Wilson in Cheung. Notwithstanding that, Justice Wilson declined to follow the decision in the formulation of her jury questions.

In response to the closing argument, made by plaintiff’s counsel in which he had suggested that the jury need only insert the same particulars of negligence under the causation question that they inserted under the standard of care question, Justice Wilson charged the jury that what they had been told was wrong in law and told the jury that they had to state how the negligence caused the infant’s brain damage.  At paragraph 65, Justice Wilson summarized the issue before the jury stating:

In a nutshell, the jury had to determine if Rhonda suffered HIE at the time of her birth and, if so, whether anything Dr. Samra and/or Dr. Ma did cause HIE. Their task was to answer the question on causation and explain the “how” part of the equation.  It was incumbent on the jury to explain the causal link in their answers. 

Justice Wilson went further, citing Professor Knutsen from Queen’s, “Coping with Complex Causal Information in Personal Injury Cases” (2013) 41: 2-3 Advoc Q. 149 at page 50, causation is “the bridge which connects the wrongdoing to the injury”.

This formulation is the best description yet of how a trier of fact is to determine whether a cause was “necessary”.  By focusing on how the injury occurred, and the link between the conduct and the outcome, the trier of fact is better placed to determine whether the role of the alleged tortfeasor is simply part of the sequence of events or whether that tortfeasor’s conduct was necessary to bring about this outcome. Answering the question “how” does not require scientific precision and, therefore, meets the analytic standard of Snell and Clements.  If the trier of fact is not able to explain how an individual defendant’s conduct caused the outcome, that defendant should not be found liable.

Conclusion

Trial counsel and those instructing them need to focus on the evidence.  How does the plaintiff intend to prove causation? What do their experts say?  Are they relying on inferences?  The Ghiassi reference back to Snell reinforces the importance that the defence must introduce “some evidence to the contrary” in order to blunt the inference drawing of the trial judge and balance the causation inquiry with an alternate theory of causation. Otherwise, it appears from very liberal use of inference drawing, that the Court is willing to fill in the gaps of missing causation evidence.