Chelsea Weekley suffered a skull fracture as an infant and underwent - surgery 17 years later.to fix it. She died, several days after the surgery, and her mother, Sandra Hall, sued the hospital and the surgeons. Hall argued that the surgery caused Weekley to suffer a seizure and die, and that the surgeons should have prescribed anti-seizure medication. But the defendants argued that no seizure had occurred and that a heart-related ailment was the likely cause of death. A jury trial was held and the jury found in the defendants’ favor.
On appeal, Hall argues that the district judge erroneously permitted three of the defendants’ experts to opine about Week-ley’s likely cause of death. We conclude that Hall forfeited her arguments as to two of these experts by making perfunctory and underdeveloped arguments concerning the experts’ testimony, qualifications, and methodology. However, we find that the third expert lacked the requisite qualifications to opine that Weekley’s heart ailment was the likely cause of death. Because there is a significant chance that the erroneous admission of this expert testimony affected the outcome of the trial, we vacate the district court’s judgment and remand for further proceedings.
I. BACKGROUND
A. Weekley’s Surgery and Death
When Chelsea Weekley was approximately five months old, she was dropped and suffered a skull fracture. As the fracture expanded over time, a cyst formed in the area. The fracture and cyst did not become a cause for concern until, at the age of 17, she was hit in the head and suffered a loss of consciousness, blurred vision, and dizziness. After CT and MRI scans confirmed the extent of the fracture and the cyst, Weekley underwent a “cra-nioplasty” surgery to repair, the fracture and the area of the dura (the thick membrane surrounding the brain) where the cyst had formed. The surgery was performed at SSM Cardinal Glennon Children’s Hospital (“Hospital”) by Dr. Ann Flannery, a neurosurgeon, and Dr. Raghu-ram Sampath, a neurosurgical resident.
Weekley’s autopsy was performed by Dr. Raj Nanduri, a board forensic pathologist. According to Dr. Nanduri, forensic pathology concerns the effect of sudden, accidental, and suicidal death on the human body.. After performing a physical, microscopic, and toxicological examination of Weekley’s body, Dr. Nanduri was unable to identify a cause of death. So she asked Dr. Mary Case, a neuropathologist, to' examine Weekley’s brain. Dr. Case found that the surgery damaged the dura and surface of Weekley’s brain. Based on this finding, Dr. Nanduri concluded that Weekley had died from a seizure brought about by the surgical damage. Neither Dr. Nanduri nor Dr. Case was aware of or had reviewed the pre-surgery CT and MRI scans when they made their findings.
B. Pre-Trial Proceedings
Weekley’s mother, Sandra Hall, sued Dr. Flannery, Dr. Sampath, and the Hospital, alleging that they provided Weekley with negligent post-operative care, and that this negligence caused Weekley to suffer a seizure and die. Before trial, Hall filed two motions in limine (“MILs”) that concerned three of the defendants’ expert witnesses: Dr. John Ruge, a pediatric neurologist; Dr. Douglas Miller, a neuropa-thologist; and Dr. Steven Rothman, a pediatric neurologist.
In MIL #48, Hall sought to bar Dr. Miller from testifying that anything other than a seizure had caused Weekley’s death, on the ground that Dr. Miller had not provided such an opinion to a reasonable degree of medical certainty. The district judge granted this MIL, though only to the extent that Dr. Miller had in fact failed to disclose any such opinion.
In MIL #49, Hall sought to bar the defendants and their witnesses from denying that Weekley’s death was caused by a seizure. In doing so, Hall argued that Dr. Ruge and Dr. Rothman were “not qualified through education or experience to give an opinion to a reasonable degree of medical certainty as to Weekley’s forensic cause of death.” In addition, Hall argued that Dr, Ruge had failed to offer any scientific explanation for his opinion that Weekley had not died from a seizure, and that Dr. Roth-man had failed to offer any cause-of-death opinions to a reasonable degree of medical certainty. The district judge denied the MIL, noting that the defendants’ experts could provide any cause-of-death opinions that had been previously disclosed.
C. Trial Proceedings
At trial, the defendants elicited cause-of-death testimony from Dr. Ruge, Dr. Miller, and Dr. Rothman. Dr. Ruge testified that Weekley’s death was not brought about by a seizure, and opined that “focal interstitial chronic inflammation” of Week-ley’s heart (i.e., thickening of the heart’s connective tissue) was the likely cause of death. Hall’s attorney objected immediately, stating,
[Tjhere’s been absolutely no foundation laid, no qualifications, nothing that would suggest that this gentleman is qualified to give, nor has that been disclosed as one of the opinions as to cause of death.
A sidebar ensued in which the parties and the district judge focused on whether Dr. Ruge had previously expressed these opin
Dr. Miller testified next. Before he shared his cause-of-death opinions, Hall’s attorney objected, stating,
The Court has already determined after argument and briefing that defendants’ expert Dr. Douglas Miller is barred from testifying, suggesting or implying that Chelsea Weekley’s cause of death was anything other than a seizure. In addition, this motion in limine was also granted that defendants’ opinion witnesses cannot express any opinions as to cause of Chelsea Weekley’s death that has [not] previously been stated to a reasonable degree of medical certainty.
The district judge concluded that although Dr. Miller had previously stipulated that he had reached his opinions with a reasonable degree of medical probability but not medical certainty, his opinions had been adequately shared before trial and thus would not constitute a prejudicial surprise to Hall. Dr. Miller then testified that “it’s overwhelmingly probable that [Weekley’s death] was not caused by a seizure.”
Finally, Dr. Rothman testified that he did not believe Weekley suffered any seizures before her death. Hall did not object to any of Dr. Rothman’s cause~of-death opinions during trial.
At the end of trial, the jury returned a general verdict “findfing] for all of the defendants and against the plaintiff.” This appeal followed.
II. ANALYSIS
Hall argues on appeal that the district court erred in permitting Dr. Ruge, Dr. Miller, and Dr. Rothman to testify about the specific cause of Weekley’s death. The admissibility of expert testimony is governed by Federal Rule of Evidence 702 and Daubert v. Merrell Dow Pharmaceuticals.,
We review de novo whether a district judge has properly followed Rule 702 and Daubert. Kunz v. DeFelice,
Even if an expert’s testimony was erroneously admitted or excluded, reversal is not warranted unless the error has affected a party’s “substantial rights.” Fed. R. Civ. P, 61; see Naeem,
A. Claim Forfeited as to Dr. Miller and Dr. Rothman
In her appellate brief, Hall states in conclusory fashion that Dr. Miller and Dr. Rothman should not have been allowed to testify that seizure was not the cause of Weekley’s death. But Hall makes no effort to explain why either doctor’s cause-of-death testimony was improperly admitted, or to identify the specific testimony that was improperly admitted. This failure is fatal, as “we are not in the business of formulating arguments for the parties.” United States v. McClellan,
Hall does cite Dr. Miller’s testimony that an epilepsy-related cause-of-death finding can be made in the absence of other potential causes such as heart attack, as well as Dr. Rothman’s testimony that clenched fists can be linked not only to seizure but also to heart attack and lung disease. However, Hall failed to take the critical next step of arguing that Dr. Miller and Dr. Rothman lacked the requisite qualifications and/or methodology to supply this testimony. Rather, Hall merely cited this testimony to underscore her contention that Dr. Ruge had supplied “wholly unfounded and baseless cause of death testimony.” See Estate of Moreland v. Dieter,
B, Reversible Error Involving Dr. Ruge
1. Rule 702¡Daubert Framework Should Have Been Applied
Hall argues that the district judge erred •in permitting Dr, Ruge to testify that Weekley’s cause of death was not attributable to seizure, and that a heart-related issue was the likelier explanation. Both Hall and the defendants contend that we should review the admission of this testimony for abuse of discretion. But that overlooks the fact that the abuse of discretion standard is available only when the district judge actually applied the Rule 702¡Daubert framework, which did not occur here.
In MIL # 49, Hall argued that Dr, Ruge offered cause-of-death opinions without being “qualified through education or experience” and without the requisite “scientific explanation.” With that challenge to Dr. Ruge’s credentials, the district judge should have conducted, a Daubert inquiry, even though Hall .did not expressly reference Daubert or Rule 702 by name. And when Hall objected at trial that “there’s been absolutely no foundation laid, no qualifications, nothing that would suggest that this gentleman is qualified to give ... opinions as to cause of death,” the district
But the objections did not prompt the judge to examine Dr; Ruge’s qualifications and methodology or to apply the Daubert test. Instead, the judge focused solely on whether the challenged opinions had been previously disclosed. Perhaps even more curiously, neither party made any effort to clarify that Hall had in fact invoked Rule 702 and Daubert, and that the district judge should therefore comment on more than whether the opinions had been previously disclosed. The parties’ failure to do so, however, did not extinguish the need to apply the Rule 702/Daubert framework to Dr. Ruge’s opinions. Because that application never occurred, our review of the admission of these opinions is de novo.,
2. Adequate Qualifications and Methodology for Dr. Ruge’s Seizure Opinion
At trial, Dr. Ruge opined that Weekley had not suffered a seizure before she died. He noted that she had no documented history of seizures, and that her body and bed did not display , the typical signs of seizure such as violent convulsions, tongue damage, and urinary incontinence. He also stated that seizures typically do not result from cranioplasty (the surgical procedure Weekley underwent), and that the cranioplasty here had not damaged Weekley’s brain.
This opinion was not erroneously admitted. For one, Dr. Ruge possessed sufficient qualifications to opine on the operation performed and the possible occurrence of a seizure afterward. At the time of trial, Dr. Ruge had practiced pediatric neurosurgery for approximately 25 years and was serving as the chief of pediatric neurosurgery for the Advocate Health Care system, which encompassed two major children’s hospitals and approximately ten other hospitals. In addition, he was certified by the American Board of Neurological Surgery, was affiliated with multiple neurological and medical societies, and was a former editorial board member for the publications Critical Reviews in Neurology and Child’s Nervous System. And perhaps most notably, he had operated on growing skulls fractures like Weekley’s, and had published articles on various pediatric neurosurgery topics including epilepsy, cranial cysts, and severe head injury.
In addition, Dr. Ruge’s seizure-related opinions were based on sufficiently reliable methodology. Dr. Ruge arrived at his conclusions based on his review of the autopsy report; Weekley’s medical records, including the MRI and CT scans taken before surgery, Dr. Flannery’s operative report, and Dr. Flannery and Dr. Sam-path’s post-surgery progress notes; and deposition testimony. See Gayton,
Hall contends that Dr. Ruge lacked the requisite qualifications because pathology is not his area of professional focus. However, this argument ignores the fact that “[o]rdinarily, courts impose no requirement that an expert be a specialist in a given field.” Gayton,
Here, the issue of whether a seizure occurred shortly before Weekley’s death did' not concern knowledge that is held solely by pathologists. Dr. Nanduri; the pathologist who examined Weekley after her death, testified that a seizure-related cause-of-death finding is made by excluding all other apparent causes, and that she arrived at her finding here based on the damage to Weekley’s dura and cortex— damage that a non-pathologist could have observed. Moreover, Dr. Ruge stated that he “routinely cared for patients who ... have seizures as part of their neurosurgical condition,” witnessed numerous seizures himself, and operated on individuals ■with head injuries comparable to Week-ley’s. So Dr. Ruge possessed the requisite qualifications to testify about seizures. See Gayton,
3. Inadequate Qualifications for Dr. Ruge’s Heart Opinion
While Dr. Ruge was qualified to opine on Weekley’s surgery and the possibility of seizure, this qualification does not extend to his opinion that Weekley’s heart-related issue was the likelier cause of death. See Gayton,
Wé do not doubt that Dr. Ruge is an intelligent doctor who possesses considerable knowledge about surgery, pediatrics, and neurology. However, the record lacks sufficient evidence demonstrating that this knowledge and the related experiences fender Dr. Ruge qualified to opine about Weekley’s heart. See Dura Auto. Sys. of Ind., Inc. v. CTS Corp.,
4. Hall’s Substantial Rights Were Affected
The fact that Dr. Ruge’s heart-related cause-of-death testimony was erroneously admitted does not automatically entitle Hall to a new trial. Rather, she must show that this error had a “substantial influence over the jury.” Farfaras,
It is undisputed that Weekley’s cause of death was a critical issue at trial. Hall pointed to seizure—a relatively difficult fact to prove since (as both parties agree) such a finding is made only by ruling out all other possible alternatives. It is no surprise that the defendants chose not only to argue that a seizure had not occurred, but also to offer an alternative cause—heart troubles. And Dr, Ruge played a critical role supporting this alternative cause, testifying about multiple studies he had read that linked the heart condition that Weekley had to the circumstances under which she passed away.
Critically, the import of Dr. Ruge’s testimony cannot be minimized on the ground that it was merely “cumulative” of testimony provided by other experts. See Naeem,
The defendants contend that reversal would be improper because “there is no basis to. conclude that admission of the Defendants’ experts’ testimony influenced the jury’s verdict.” They argue that even if the jury had not heard any testimony from the defendants’ experts "regarding alternative causes of death, the jury could have found for the defendants on the grounds that they did not breach their standard of care, or that any such breach did not cause Weekley’s death. In support, the defendants cite several Illinois state court decisions that found a new trial to be unnecessary where it was possible that the jury’s verdict rested on an issue that was not subject to appeal. See Tabe v. Ausman,
But state law is not applicable to this inquiry. “In this circuit the harmlessness standard is treated as procedural -and therefore in a diversity case is governed by federal law and [Rule] 61.” Sokol Crystal Prods., Inc. v. DSC Commc’ns Corp.,
III. CONCLUSION
We Reverse the district judge’s decision to admit Dr. Ruge’s heart-related cause-of-death testimony, Vacate the judgment, and Remand the case for proceedings consistent with this opinion.