By Michael Hoenig - New York Law
Journal - May 9, 2016
Just weeks ago, on April 25, a U.S. Court of Appeals for the First Circuit
panel split 2-1 on whether a claimant's expert on specific
causation in a toxic tort case offered opinions that were
sufficiently reliable under Federal Evidence Rule 702 to
withstand exclusion. The case is
Milward v. Rust-Oleum,1 a claim by a pipefitter
and refrigerator technician who, over 30 years, was exposed to
varying levels of benzene from paints and other products made by
the (sole remaining) defendant, Rust-Oleum. Brian Milward, the
plaintiff, was diagnosed in 2004 with Acute Promyelocytic
Leukemia (APL) and sued a number of defendants, contending that
their negligence caused his disease.
In 2009, the district court excluded Milward's general causation expert but
that ruling was reversed on appeal,2 so the focus in
the trial court on remand shifted to Rust-Oleum's challenge
regarding Milward's specific causation expert, Dr. Sheila
Butler, an occupational medicine physician. As many readers of
this column know, in a toxic tort case the plaintiff must
establish, through expert testimony, both general and specific
causation. In this case, therefore, that meant a sufficiently
reliable showing that exposure to benzene can cause APL (general
causation) and that, in fact, benzene exposure was a substantial
factor in the development of Milward's APL (specific causation).
The instant appellate ruling involved the district court's
rejection of Butler's specific causation opinions.
This column has frequently reported on federal and state "gatekeeping"
decisions in which courts have determined whether expert
opinions were "reliable" enough to pass
Frye4 admissibility criteria. Less than two
months ago, my March column, "Experts Flunk Reliability Test in
BMW Case,"5 reported on the New York Court of
Appeals' decision in a toxic tort case claiming damages to a
child from in utero exposure to unleaded gasoline vapor
allegedly caused by an automobile's defective gas hose. The
endnotes in that column listed many prior articles on expert "gatekeeping"
issues. So, why should this column focus afresh and so soon on
the expert reliability/causation calculus?
The reason is that the April 25 First Circuit ruling in Milward (by
a 2-1 vote) tees up very well some critical tensions in toxic
tort experts' methodologies and presents crossroads Daubert and
Frye issues that recur. For example, experts can and do rely
upon scientific and technical literature. But what if the
articles relied upon are themselves partially or wholly
unreliable? Or, what if there is inconsistent technical
literature, that is, other articles at odds with those favored
by the testifying expert? Can the expert simply select the line
of literature that supports his position in the case without
explaining the reasons for that choice in a manner consistent
with reliable methodology?
Does "cherry-picking" favorable articles sufficiently create a jury
question, leaving the adverse literature to be explored on
cross-examination or introduced during the adversary's case? Or
does the problem of conflicting literature go to the heart of
the threshold "reliability" question inherent in Daubert
admissibility criteria? And, what should a court do when the
expert is, let's say, " too selective"? These are some of the
tensions reflected in the Milward decision.
The majority and dissenting opinions are relatively brief, well-written and
quite readable, despite the technical subject matter. The
pivotal shortcomings in the expert's methodology (as elaborated
by the majority) offer litigators valuable lessons in
challenging or defending expert opinions, lessons that apply to
experts' battles even outside the arena of toxic torts.
The vulnerabilities identified in Milward also inform readers on
questions relevant to retention of suitable experts, preparing
them for the "reliability" fray sure to come and structuring
advocacy on such issues. The dissenting opinion presents a
differing point of view which, too, needs to be understood.
Therefore, let us take a closer look at this new Milward
As noted above, plaintiff's theory was that benzene exposure caused his APL
disease. His specific causation expert, Dr. Butler, was an
employee of the Veterans Administration, specializing in
clinical assessments of environmental and occupational exposure
in combat-exposed veterans. The dissenting judge, particularly,
was impressed by her qualifications. "She has quite the CV," he
said, and proceeded to enthusiastically elaborate her
qualifications.6 But Butler's qualifications were not
the issue. Were her theories "reliable" under Federal Evidence
Rule 702 and Daubert's admissibility criteria? That was
the focus by the appellate panel majority. Remember, the issue
was specific causation, i.e., did the exposure to benzene cause
this disease to this person?
Butler presented three theories. First, she testified that, although
benzene is naturally occurring, "there is no safe level of
benzene exposure." This was her predominant theory, and "she
consistently reiterated her hypothesis," said the court.7
She emphasized that she reached this conclusion by examining
"the biology, the pathophysiology, what the substance does to
the person and the disease process." She was able to do so
without relying on any of the relevant epidemiological studies.
Given this no-safe level position, Butler maintained that Milward's
exposure (as detailed by an industrial hygienist expert who had
calculated the benzene levels in products plaintiff used) was
likely the cause of his APL. The district court rejected this
no-safe level hypothesis because it could not properly be tested
by any known rate of error—a conclusion the appellate panel
assumed was correct.8
Butler offered a second "rather cursorily concluded" position, as described
by the court, beyond the no-safe level hypothesis. She contended
that an individual's "relative risk" of developing APL increases
when exposed to specified amounts of benzene. She then compared
Milward's exposure levels to those that had been found to be
dangerous in studies reporting that research. Since Milward's
exposure levels (as calculated by plaintiff's industrial
hygienist expert) were higher than those found to be dangerous
in selected literature, Butler reasoned that benzene exposure
was the likely cause of plaintiff's APL.
However, Butler did not explain why she chose the studies on which she
relied, nor did she address any study with contrary findings.
During her deposition she was asked, "Are you aware of any
studies which find there is no relationship between benzene
exposure and APL?" She responded, "Yes…the literature has
support for both." Then counsel asked, "Do you intend in this
case to weigh the different epidemiological studies and offer an
opinion as to which ones we should rely on and which ones we
should discount?" Butler replied, "No."9
Finally, Butler engaged in a "differential diagnosis" to conclude that
benzene exposure likely caused Milward's APL. This method is
essentially a process of elimination. Thus, she "ruled out" some
of the more common factors associated with APL, among them
obesity and smoking. She then determined that, since benzene
exposure was a potential cause, she could also "rule out" an
idiopathic diagnosis, that is, a diagnosis without a known
cause. Thus, since benzene exposure was the "only significant
potential cause remaining," Butler concluded that it likely was
The district court rejected each theory. On appeal, plaintiff did not rely
on the "no-safe level" hypothesis (Butler's first and
predominant theory). Instead, Milward pressed on appeal the
second conclusion based on "relative risk" and Butler's third
theory, "differential diagnosis." The appellate court grappled
with those. Butler's "relative risk" methodology was
problematical because she expressly disavowed her intent to
analyze conflicting epidemiological studies. Here, a number of
studies showed a "correlation between APL and benzene exposure
at a specific level, while other studies do not show that
In order to establish specific causation by the relative risk method,
Butler was required to choose a study, or studies, "to serve as
a baseline" to which she could then compare Milward's case. But
while one study showed a correlation at exposure levels lower
than Milward had experienced, another study exhibited no such
correlation even at exposure levels higher than the plaintiff's.
Thus, the latter study yielded "a vastly different comparison."11
Given that Butler had "anchored her testimony to her no-safe threshold
hypothesis," a theory that did not turn on the validity of any
of the epidemiological studies, it was consistent for her to
state that she had neither the need nor intent to compare the
competing literature. When an expert's medical opinion is
grounded exclusively on scientific literature, the "gatekeeper"
trial court has discretion "to require the expert to explain why
she relied on the studies that she did and, similarly, why she
disregarded other, incompatible research," noted the court.12
When an expert engages in a relative risk analysis, in the manner Butler
did here, the district court "is on firm ground in requiring
such an explanation, since the validity of the approach depends
on the reliability of the studies chosen." If the expert is
comparing the plaintiff's condition to a study, and the study is
based on an unreliable methodology, then "the comparison itself
is futile." Here, the relevant studies were not only in tension
with one another, "but expressly cast each other into doubt."
Butler's "complete unwillingness" to engage with the conflicting
studies (whether she was able to or not) made it "impossible"
for the district court "to ensure that her opinion was actually
based on scientifically reliable evidence and, correspondingly,
that it comported with Rule 702."13
The "differential diagnosis" opinion likewise had shortcomings. Butler had
"ruled out" obesity and smoking as causes of Milward's APL. But
the district judge was concerned about the utility of Butler's
approach "given the high percentage of APL cases that are
idiopathic"—according to the record, roughly 70-80 percent of
all APL diagnoses. The district judge also concluded that
Butler's reasoning was "circular." She "ruled out" an idiopathic
APL by "ruling in" benzene as a cause, but she failed to provide
a scientifically reliable method of "ruling in" benzene in the
first instance. When "differential diagnosis" is used, it must
be shown that the steps taken as part of that analysis—the
"ruling out" and the "ruling in" of causes—were accomplished
utilizing scientifically valid methods.14
Since Butler was only able to rule out an idiopathic APL because she had
"ruled in" benzene as a cause, the validity of her differential
diagnosis "turns on the reliability of that latter conclusion."
The reliability of that decision was "particularly critical here
given the extensive number of APL cases that are idiopathic."
Indeed, Butler seems to have "ruled in" benzene exposure solely
by relying on her other two theories.
But the district court found both of those to be unreliable, and the
appellate majority did not disagree. Thus, plaintiff had failed
to show how Butler could have reliably utilized either method to
"rule in" benzene exposure. The expert needed some other method
to "rule out" an idiopathic diagnosis. She did not provide one.
As such, the district court acted within its discretion in
excluding the opinions, and the summary judgment in favor of
Rust-Oleum was correctly granted.15
The Milward decision is instructive reading for litigation specialists,
whether representing plaintiffs or defendants. On one level, it
teaches that even highly qualified experts, in this case a
strongly opinionated medical specialist, must hew to the
reliability standards required by Daubert and Federal
Evidence Rule 702. The entire episode teaches that expert
credentials do not substitute for the reliable methodologies
that, when challenged, have to be specified.
On another level, Milward teaches that experts' cherry-picking among
competing epidemiological or scientific studies is likely to be
exposed by attentive, opposing counsel. Therefore, an expert's
decision to rely on one study but reject a contradictory study
requires reliable, non-speculative reasoning. An expert's choice
based on personal preference, belief, assumptions or hunches
will not suffice.
1. 2016 U.S. App. LEXIS 7470 (1st Cir. April 25, 2016).
2. See Milward v. Acuity Specialty Prods. Group, 639
F.3d 11 (1st Cir. 2011).
3. Daubert v. Merrell Dow Pharms., 509 U.S. 579 (1993).
4. Frye v. United States, 293 F. 1013 (1993).
5. NYLJ, March 15, 2016, p. 3.
6. Milward, 2016 U.S. App. LEXIS 7470, at *18-*20
7. Milward, LEXIS, at *4.
8. Id. LEXIS, at *4. The plaintiff did not "meaningfully
challenge" that ruling on appeal so the appellate court assumed
it was correct and bypassed further discussion.
9. Id. LEXIS at *5.
10. Id. LEXIS at *5-*6.
11. Id. LEXIS at *9-*11.
12. Id. LEXIS at *11-*12.
13. Id. LEXIS at *13-*14.
14. Id. LEXIS at *15-*17.
15. Id. LEXIS at *15-*18.
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