Successfully Excluding Treating Physicians’ Opinions under Daubert
It is well settled that in a personal injury case the plaintiff has the burden to prove that the accident caused the plaintiff’s claimed injuries and the resulting damages. Although a plaintiff can testify as to the existence of pain, expert medical testimony is generally required as to the cause of such pain.
In all but the most straightforward of cases (such as a broken limb, for example), the cause of an injury involves technical, scientific, or medical matters which are beyond the common knowledge or experience of jurors. Thus, to prove causation, personal injury plaintiffs are nearly always required to utilize the testimony of post-accident treating physicians to render expert opinions that the accident caused their injuries and necessitated the treatment the plaintiffs sought for those injuries. As expert witnesses, plaintiffs’ treating doctors who are utilized in support of their claims are subject to the Daubert standard for expert testimony under Wis. Stat. § 907.02(1).
The conventional wisdom among personal injury lawyers seems to be, however, that treating doctors are either immune from the Daubert standard or are somehow less vulnerable to its requirements than other expert witnesses, such as engineers or vocational experts. The purpose of this article is to show how and why that is wrong. Applying well-established case law from the federal courts interpreting the Daubert standard, there are several arguments that can effectively be made, and should more frequently be made, to either limit or outright bar a plaintiff’s treating doctor from testifying at trial. The authors of this article have had success in doing so, and describe the tactics that they have found to be most effective. Defense lawyers are encouraged to more frequently consider securing court rulings under Daubertregarding the opinions of treating medical experts at the pretrial motion stage using the arguments set forth in this article.
I. Daubert in Wisconsin
Under Wisconsin law, expert testimony is admissible only if “scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue.” The expert testimony must be “based upon sufficient facts or data,” and “the product of reliable principles and methods” applied “reliably to the facts of the case.” Wis. Stat. § 907.02(1) adopts the federal Daubert standard for the admissibility of expert testimony. Under the Daubert standard, an expert witness’s testimony is not admissible unless “the expert’s reasoning or methodology underlying the testimony [is] scientifically reliable.” Daubert also requires the expert to rely on “facts or data,” as opposed to subjective impressions.
Daubert imposes an important “gate keeping” function for expert testimony, which entails determining whether the proposed expert testimony is reliable and ensuring only helpful, legitimate expert testimony reaches the jury. In deciding whether an expert's opinions are based on reliable principles and methods, the Court may consider a wide range of factors, including, but not limited to:
1. Whether the expert's technique or theory can be or has been tested—that is, whether the expert's theory can be challenged in some objective sense, or whether it is instead simply a subjective, conclusory approach that cannot reasonably be assessed for reliability;
2. Whether the technique or theory has been subject to peer review and publication;
3. The known or potential rate of error of the technique or theory when applied;
4. The existence and maintenance of standards and controls; and
5. Whether the technique or theory has been generally accepted in the scientific community.
Additional reliability factors have been recognized in other federal cases:
1. Whether experts are “proposing to testify about matters growing naturally and directly out of research they have conducted independent of the litigation, or whether they have developed their opinions expressly for purposes of testifying”;
2. Whether the expert has unjustifiably extrapolated from an accepted premise to an unfounded conclusion;
3. Whether the expert has adequately accounted for obvious alternative explanations;
4. Whether the expert “is being as careful as he would be in his regular professional work outside his paid litigation consulting”; and
5. Whether the field of expertise claimed by the expert is known to reach reliable results for the type of opinion the expert would give.
Importantly, it is the proponent of the expert’s testimony—i.e., the plaintiff in a personal injury case when the expert is a treating medical provider—who has the burden of proof to show that the expert’s testimony satisfies the Daubertstandard. It is not the burden of proof of the party challenging the testimony—i.e., defendants in an injury case—to show that it does not.
In nearly every case, a plaintiff’s treating medical provider has focused only on treating the condition as it presents, and rarely takes the time and effort to complete the steps required by Daubert to determine the actual cause of the underlying condition. Consequently, the requirements of Daubert provide several methods of attacking a treating physician’s opinions. However, to set up a successful Daubert challenge, defense counsel must first obtain and thoroughly review the plaintiff’s medical records and then carefully depose the physician. With that in mind, the next sections discuss tactics for challenging treating doctors under the Daubert standard.
II. Challenging a Treating Medical Provider’s Opinions Based on a False Factual Premise
One of the most effective ways to attack a treating physician’s opinions under Daubert is when those opinions are based upon an incomplete, if not outright wrong, understanding of the plaintiff’s pre- and post-accident medical history. Pursuant to the plain language of the statute, an expert witness’s testimony is not admissible if it is not “based upon sufficient facts or data” and is not “the product of reliable principles and methods” applied “reliably to the facts of the case.” Indeed, federal courts interpreting the Daubert standard routinely disqualify experts from testifying when their opinions are based upon a false or otherwise incorrect understanding of the facts underlying their opinions.Importantly, defense counsel can and should rely upon those cases in Wisconsin state courts because the Daubert standard is a federal standard that our legislature has adopted, so those federal cases are considered persuasive authority.
That being the case, if a medical provider has rendered a causation opinion that assumes, for example, that a plaintiff had no relevant pre-existing history based solely on representations from the plaintiff taken during a history (i.e., the plaintiff’s own description), yet the plaintiff’s medical records reflect that the plaintiff did in fact have such a history, then the provider’s opinions are arguably not based upon sufficient facts or data and were not reliably applied to the facts of the case. This is a sound basis to seek disqualification of that expert’s opinions under Daubert.
In addition, a doctor’s opinions may be subject to exclusion where his or her understanding of a plaintiff’s history, while not necessarily incomplete, is nevertheless based upon per se unreliable information. An example is where a doctor has not reviewed or been provided with the plaintiff’s pre-accident records, but has been told by the plaintiff’s counsel what those records allegedly reflect. Federal courts have routinely held that information purporting to summarize evidence but created primarily or solely by plaintiff’s counsel or staff carries a per se inference of bias that prevents opinions relying upon that information from being considered admissible.
In a case where the authors recently successfully excluded a plaintiff’s treating doctor from testifying by prevailing on a Daubert motion, the doctor’s opinions all relied on the assumption that the plaintiff had no prior history or complaints of the conditions she claimed were caused by the accident—tension headaches and neck pain. This assumption was based solely upon the plaintiff’s representations to her doctor during her medical appointments. However, from a careful record review, it was clear the plaintiff had a long, relevant, and recent history of sporadic muscular neck complaints and tension headaches. The treating physician had either missed this history, or, as is more likely the case in most personal injury lawsuits, had simply not reviewed or been provided with the plaintiff’s pre-accident medical records, and instead relied solely on plaintiff’s statements.
Confronted with this scenario, there are at least two approaches available to defense counsel in taking the doctor’s deposition. The first is to simply have the doctor confirm that he or she has relied solely upon the plaintiff’s statements and assumed no relevant pre-accident history. That is, get the doctor nailed down on the notion that his or her opinions rely on assumptions that are demonstrably false. The second—and this is admittedly a little bit more unpredictable an approach as it runs the risk of allowing the doctor to correct the errors in his or her opinions on the fly—is to confront the doctor with the false assumptions underlying his or her opinions and have the doctor hypothesize how correcting those false assumptions may impact his or her opinions.
In our case, when we deposed the treating physician, we went with the latter, higher risk option, and it paid off. We asked her if her opinions would change if she assumed that there was a prior history that directly contradicted her assumptions (again, there clearly was such a history based upon the records). In response to this, the treating physician acknowledged that her opinions on the cause of the plaintiff’s injuries would no longer be valid if the plaintiff had a pre-existing history of any of the complaints that she related to the accident. This testimony was particularly important, because often, plaintiff’s counsel will argue that challenging the underlying facts of a doctor’s opinions does not warrant excluding the opinions but rather is best left to challenge upon cross-examination. In our case, we were able to argue that the doctor herself admitted that her false factual premise rendered her causation opinions unreliable and therefore inadmissible. Again, an alternative, lower-risk but also lower-reward approach would simply have been to exhaust the doctor’s own assumptions in her deposition, without confronting her with the incorrectness of them and giving her an opportunity to correct them, and instead leave that argument for the motion itself by showing the doctor’s erroneous assumptions through the certified medical records. There is no denying, however, that a judge will find compelling an expert admitting under oath that his or her opinions would be wrong in a hypothetical scenario that you can conclusively demonstrate is true. In our case, the fact that the treating medical provider’s opinions relied upon a demonstrably false factual foundation also allowed us to set up a challenge to the doctor’s methodology, discussed in the next section.
III. Challenging a Medical Provider’s Failure to Use the Correct Method to Determine Causation—Etiology Versus Diagnosis
When an injured person is seen by a doctor, the doctor’s focus is generally on diagnosing the patient’s condition—i.e., figuring out what the problem is. To the extent that the cause of that problem is relevant to the determination of what the problem is, the doctor may care about the cause. To the extent the cause is irrelevant, the doctor does not care—i.e., once the problem is diagnosed and the appropriate treatment identified, if the cause need not be known to make the diagnosis or determine the treatment, the doctor is generally not going to place a significant emphasis on the cause. For example, if a patient comes in with a broken arm, it is not necessarily of any significant importance to the diagnosis and treatment of that injury that it came as the result of a fall, a sports injury, a bar brawl, etc. Once the injury is diagnosed and the treatment identified, there is little reason for the doctor to focus on what caused the injury. For our purposes, this is the fundamental disconnect between what a doctor’s focus is on when they are treating a patient and what they are asked to do by personal injury plaintiffs or their attorneys once a claim is made.
Diagnosis is the process of identifying what a medical condition is, and the process of differential diagnosis, the accepted methodology for making a diagnosis, is for the doctor to first rule in all of the potential conditions that could explain the patient’s condition, and then to progressively rule out those conditions as additional information about the condition is obtained.
The science of determining the cause of a medical condition is not diagnosis; it is etiology. And, like differential diagnosis, there is also a scientific method in the medical field for determining the etiology of a particular condition. It is analogous to differential diagnosis, and perhaps not surprisingly, is called differential etiology. The difference is that, rather than focusing on what the condition is and how to treat it, as diagnosis does, etiology focuses on what caused it, and differential etiology involves the process of ruling in all of the possible causes that could result in a particular condition (to establish general causation), and then to progressively rule out the causes that could not explain the condition, one by one, as additional information is obtained (to establish specific causation).
This distinction is incredibly important in personal injury cases because, in nearly every case confronted by defense counsel, the plaintiff’s treating medical providers who are proffered as experts will have diagnosed the plaintiff’s condition, presumably by way of differential diagnosis (though if they have not that is another problem in and of itself), but it is very rare that the plaintiff’s treating doctor will have conducted a differential etiology, because again, a doctor treating a patient is focused on determining what the condition is and how to treat it, not necessarily what caused it. The cause—i.e., the etiology—of a particular condition is only important in circumstances where that cause is relevant to the diagnosis. In personal injury cases, in the Daubert context, it is arguable that a doctor’s causation opinion where he or she has not conducted a differential etiology—the medically accepted method for determining the cause of a particular condition—is not “the product of reliable principles and methods” under Wis. Stat. § 907.02(1).
Importantly, many federal courts, including the Seventh Circuit, have made it clear that an expert must perform a “differential etiology” in order to reach a reliable causation opinion. The failure to apply the method of differential etiology in order to rule out obvious potential alternative causes is “fatal” to a doctor’s causation opinions.The fact that most doctors in their everyday practice have no significant need to apply a differential etiology, and therefore do not, yet Daubert arguably requires them to do so in order to render admissible medical causation opinions, provides fertile ground for attacking a treating physician’s opinions.
In our case, in addition to arguing that plaintiff’s doctor’s opinions were based on a false factual premise, we also challenged her opinions by arguing that she failed to perform a differential etiology by failing to consider other causes of the plaintiff’s alleged neck pain and tension headaches, including obesity, posture, other lifestyle factors, anxiety, and stress. In response to that line of questioning, the plaintiff’s treating doctor admitted in her deposition that the plaintiff had many other conditions that were also possible causes of neck pain and tension headaches. However, the doctor failed to account for how these alternative causes factored into her opinions in both her report and her deposition, and also acknowledged that she had never specifically undertaken to rule them out as causes. That is, she essentially acknowledged that she had failed to apply a differential etiology to determine the cause of the plaintiff’s symptoms. As a result, in our Daubert motion, we argued that the physician’s failure to perform a differential etiology and rule in or rule out other alternative causes of plaintiff’s complaints was an additional reason that her opinions were unreliable and inadmissible. We identified the following Daubert and Seifert factors in particular: 1. The physician’s method for determining cause was not generally accepted by the medical community; 2. The physician’s method unjustifiably extrapolated from an accepted premise to an unfounded conclusion; and 3. The physician had not adequately accounted for obvious alternative explanations. In essence, without performing a differential etiology, we argued the physician impermissibly offered only an ipse dixit opinion, asking us to “take her word for it.” This argument was an additional basis for the court in granting our Daubert motion excluding the doctor’s testimony.
IV. Challenging Medical Causation Opinions that Are Based on a Temporal Relationship Alone—the Post Hoc Ergo Propter Hoc Fallacy
This last section discusses a scenario that is likely very familiar to all defense counsel: A plaintiff claims that she has no pre-existing history of a particular condition, and the medical records reflect that she never treated for anything similar to it prior to the accident. Then, following the accident, she begins to complain of symptoms that she relates to the accident. Based solely on these facts, and nothing more, her treating doctor provides a causation opinion: “Since the patient claims no prior history of these symptoms and her records reflect no prior treatment for them, and given that her complaints have been consistent since the accident, it is my opinion to a reasonable degree of medical certainty that the accident is the cause of the patient’s current complaints.”
Cases like this are routine for defense counsel, and where there really is no record of a pre-existing history, the temptation may be to simply accept that causation is clearly established. This does not necessarily have to be the case. First, as discussed in the previous section, even in the scenario described here, plaintiff should still be required to show that the doctor performed a differential etiology before this causation opinion should be considered admissible under Daubert.
Second, it is well-established among the federal courts in the Daubert context that basing a causation opinion solely upon a temporal relationship is inadmissibly unscientific, as it is based on a logical fallacy known as the post hoc ergo propter hoc fallacy. An example of the fallacy is as follows: “The rooster crows immediately before sunrise, therefore the rooster causes the sun to rise.” When a doctor renders a causation opinion as follows—she did not have it before the accident and does have it after the accident, therefore the accident caused it—that doctor’s opinion is an example of the post hoc ergo propter hoc fallacy and, without more, must be considered inadmissible. Indeed, one of the specific purposes of the Daubert scientific reliability standard is to ensure “that [jurors] will not be misled by the post hoc ergo propter hoc fallacy.” In fact, it is precisely because a causation opinion like the one described here has a certain degree of attractiveness—i.e., it seems to make sense, even though it is completely unscientific—that it is a very dangerous opinion to allow the jury to hear without first challenging it by Daubert motion.
Importantly, that a temporal relationship alone is insufficient to sustain a finding of medical causation under Daubert is well-settled and has been discussed at some length by the federal courts. Reliance upon these cases as persuasive authority is appropriate given that, as noted above, Wisconsin has adopted the federal Daubert standard wholesale.Defense counsel are urged to more regularly challenge medical opinions supported solely on a temporal relationship.
The physician’s deposition is a crucial tool to establish that a physician’s sole basis for causation is a temporal relationship by exhausting all the reasons that the physician relates the injuries to the accident. In the experience of this article’s authors, that a doctor’s opinion is based solely upon a temporal relationship and nothing more happens with surprising frequency. In addition, it is critical to obtain deposition testimony that the physician does not have sufficient knowledge of the facts of the accident, such as the speed of the cars, direction of the cars, how the accident happened, and how the plaintiff’s body moved inside the vehicle. This will confirm that the doctor lacks knowledge concerning the mechanism and physics behind the accident to sufficiently explain the plaintiff’s mechanism of injury. Particularly in the context of a low velocity impact, the doctor’s lack of knowledge of these facts, combined with reliance solely upon a temporal relationship, can make a Daubert motion even more persuasive. In addition, where a biomechanical expert has been retained by defense counsel, illustrating the lack of expertise in injury causation that most medical doctors possess can further help to bolster the motion. Regardless, a medical causation opinion based solely upon a temporal relationship is per se inadmissible pursuant to the extensive federal case law addressing this issue, and defense counsel are encouraged to more regularly advance this argument given how frequently it will be available.
Contrary to popular belief, a Daubert motion against a plaintiff’s treating medical expert is not a lost cause. Indeed, in the appropriate case, a successful motion will even be dispositive, because it will deprive plaintiff of the ability to prove an essential element of his or her claim—causation. Even if unsuccessful, a strong Daubert challenge can still be used to narrow the issues for trial, educate the court about the evidence, and, where appropriate, apply valuable pressure to the plaintiff at a critical point in the case to leverage a better settlement position.
Andrew Hebl is a partner in Boardman & Clark’s Litigation Practice Group. He also chairs the firm’s Technology Committee. In addition, Andrew is currently serving as the President-Elect of the Wisconsin Defense Counsel (Wisconsin’s defense bar). Andrew’s trial and appellate practice focuses on the representation of insurance companies and their insureds. The cases primarily involve personal injury, property damage, and professional malpractice. Andrew also frequently represents insurance companies in insurance coverage disputes and extra-contractual litigation (bad faith). Finally, Andrew regularly defends municipalities in a wide variety of matters, including major civil rights lawsuits. Andrew is admitted to practice before all Wisconsin state and federal trial and appellate courts and is rated AV-Preeminent by Martindale-Hubbell.
Kathryn A. Pfefferle is a second-year litigation associate at Boardman Clark where she practices primarily in insurance defense, real estate, and construction law. Having spent five years in nonprofit management at a major domestic nonprofit, Kathryn is dedicated to pro bono work, which allows her to gain valuable hands-on trial experience and better serve her clients. Kathryn was recognized for her pro bono efforts in 2019 with the Dane County Bar Association’s Individual Attorney Pro Bono Award. Also in 2019, Kathryn was named to the Wisconsin Super Lawyers Rising Stars list. Outside her practice, Kathryn is active in the legal community and is a member of a number of legal associations, including the James E. Doyle American Inns of Court for which she serves on the executive committee as the Social Chair.
 Ollman v. Wis. Health Care Liab. Ins. Plan, 178 Wis. 2d 648, 667, 505 N.W.2d 399, 405 (Ct. App. 1993).
 Wis. Stat. § 907.02(1) (2017-18) states in full: “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, if the testimony is based upon sufficient facts or data, the testimony is the product of reliable principles and methods, and the witness has applied the principles and methods reliably to the facts of the case.”
 Ervin v. Johnson & Johnson, Inc., 492 F.3d 901, 904 (7th Cir. 2007) (citing Daubert v. Merrell Dow Pharm., Inc., 509 U.S. 579 (1993)).
 Daubert, 509 U.S. at 589.
 Fed. R. Evid. 702 advisory committee note to 2000 amendments.
 See id. (citations omitted).
 United States v. Frazier, 387 F.3d 1244, 1260 (11th Cir. 2004); see also State v. Chitwood, 2016 WI App 36, ¶ 35, 369 Wis. 2d 132, 879 N.W.2d 786 (the proponent of expert testimony has the burden to demonstrate that the proffered opinions are reliable).
 Wis. Stat. § 907.02(1).
 Berk v. St. Vincent's Hosp. and Med. Ctr., 380 F. Supp. 2d 334, 353 (S.D.N.Y. 2005) (“Because [the expert's] opinion rested on a faulty assumption due to his failure to apply his stated methodology ‘reliably to the facts of the case,’ [his] expert opinion . . . was not based on ‘good grounds.’” (internal citations omitted) (quoting Amorgianos v. Nat’l R.R. Passenger Corp., 303 F.3d 256, 269 (2d Cir. 2002)); Macaluso v. Herman Miller, Inc., No. 01 Civ. 11496, 2005 WL 563169, at *8 (S.D.N.Y. Mar. 10, 2005) (concluding that an expert's testimony must be excluded under Daubert because it is “based on incorrect factual assumptions that render all of his subsequent conclusions purely speculative”).
 See State v. Evans, 2000 WI App 178, ¶ 8 n. 2, 238 Wis. 2d 411, 617 N.W.2d 220 (“[W]here a state rule mirrors the federal rule, . . . federal cases interpreting the rule [are] persuasive authority.”).
 Lyman v. St. Jude Med. S.C., 580 F. Supp. 2d 719 (E.D. Wis. 2008) (excluding as unreliable expert testimony where the expert did not independently verify the source and accuracy of the data but rather accepted a summary from the defendant's attorney); In re TMI Litig., 193 F.3d 613, 683-84, 698 (3rd Cir. 1999) (excluding expert testimony that was based on summaries of medical histories prepared by employees of the plaintiff's lawyer); Crowley v. Chait, 322 F. Supp. 2d 530 (D.N.J. 2004) (excluding expert testimony where the testimony relied upon summaries prepared by plaintiff's counsel of depositions that had been taken in the case); Sommerfield v. City of Chicago, 254 F.R.D. 317 (N.D. Ill. 2008) (same).
 “Differential diagnosis” refers to the process of reasoning they use to identify a patient's condition. “Differential etiology” refers to the science and study of the causes of a condition, and differential etiology is the more precise term for determining which of several possible causes is the most likely cause of the plaintiff's injuries. William P. Lynch, Doctoring the Testimony: Treating Physicians, Rule 26, and the Challenges of Causation Testimony, 33 Rev. Litig. 249, 309–10 (2014).
 Brown v. Burlington N. Santa Fe Ry. Co., 765 F.3d 765, 773 (7th Cir. 2014) (citing Myers v. Ill. Cent. R.R. Co., 629 F.3d 639, 644 (7th Cir. 2010).
 Feit v. Great W. Life & Annuity Ins. Co., 271 Fed. Appx. 246 (3d Cir. 2008); Hendrix v. Evenflo Co., 609 F.3d 1183 (11th Cir. 2010); Cooper v. Marten Transp., LTD., 539 Fed. Appx. 963 (11th Cir. 2013); Wilson v. TASER Int’l, Inc., 303 Fed. Appx. 708 (11th Cir. 2008).
 Lynch, supra note 14.
 Brown, 765 F.3d at 773; Bland v. Verizon Wireless, L.L.C., 538 F.3d 893 (8th Cir. 2008); Bowers v. Norfolk S. Corp., 537 F. Supp. 2d 1343 (M.D. Ga. 2007). Decisions on claims brought under the Federal Employers’ Liability Act, which require a plaintiff to prove all elements of a negligence claim against their employer, provide a dearth of opinions analyzing the proper application of differential etiology in a Daubert challenge to a medical opinion. See, e.g., Brown, 765 F.3d at 773; Kopplin v. Wis. Cent. Ltd., 914 F.3d 1099, 1101–05 (7th Cir. 2019); Myers, 629 F.3d at 645 (7th Cir. 2010).
 Brown, 765 F.3d at 773.
 Seifert v. Balink, 2017 WI 2, ¶¶ 73-74, 372 Wis. 2d 525, 888 N.W.2d 816.
 See Gen. Elec. Co. v. Joiner, 522 U.S. 136, 146 (1997) (holding that “opinion evidence that is connected to existing data only by the ipse dixit of the expert” is inadmissible).
 See Post hoc ergo propter hoc, Wikipedia.com, http://en.wikipedia.org/wiki/Post_hoc_ergo_propter... (last visited June 10, 2020).
 Ohio v. U.S. Dep’t of the Interior, 880 F.2d 432, 473 (D.C. Cir. 1989).
 Guevara v. Ferrer, 247 S.W.3d 662, 667-68 (Tex. 2007) (“[T]emporal proximity alone does not meet standards of scientific reliability and does not, by itself, support an inference of medical causation.”) (collecting federal case law); see also, e.g., McClain v. Metabolife Int’l, Inc., 401 F.3d 1233, 1243 (11th Cir. 2005) (concluding that a temporal relationship does not, by itself, establish causation, and rejecting “the false inference that a temporal relationship proves a causal relationship”); Rolen v. Hansen Beverage Co., 193 Fed. App’x 468, 473 (6th Cir. 2006); Porter v. Whitehall Labs., 9 F.3d 607, 611 (7th Cir. 1993); see also Roche v. Lincoln Prop. Co., 278 F. Supp. 2d 744, 764 (E.D. Va. 2003) (“An opinion based primarily, if not solely, on temporal proximity does not meet Daubert standards.”); In re Breast Implant Litig., 11 F. Supp. 2d 1217, 1238-39 (D. Colo. 1998) (“[A] temporal relationship by itself, provides no evidence of causation. . . . The fact of a temporal relationship establishes nothing except a relationship in time. Proof of a temporal relationship merely suggests the possibility of a causal connection and does not assist Plaintiffs in proving medical causation.”); Schmaltz v. Norfolk & W. Ry., 878 F. Supp. 1119, 1122 (N.D. Ill. 1995) (“It is well settled that a causation opinion based solely on a temporal relationship is not derived from the scientific method and is therefore insufficient to satisfy the requirements of [Daubert].”).
 See Evans, 238 Wis. 2d 411, ¶ 8 n. 2.