Causation Determination in Workers’ Compensation
and Toxic Tort Cases.
Jon T. O’Neal, MD, MPH
Physicians with minimal knowledge of and no training in medical causation
determination are often hired to be expert witnesses. The more respected (and often more
expensive) medical clinician, researcher, or teacher brought on to a case, the more
surprising it will be during the hearing, arbitration, or trial, when it’s revealed that the
expert’s faulty causation determination was based solely on personal experience and
opinion. A recent trilogy of Supreme Court decisions on admissibility of expert
testimony has helped clarify the legal aspects of medical causation determination. 1 This
article will present a pragmatic overview of medical and legal causation, set a framework
for understanding these recent Supreme Court decisions, and help guide selection of
physicians that are most able to help lawyers, judges, and juries, make appropriate
causation determinations.
PART ONE
Medical v. Legal Causation
In the Workers’ Compensation arena establishing causation means identifying the most
probable cause of a worker’s condition or disability, and also demonstrating that it arose
out of the work or workplace. 2 Most medical literature uses the term Causation Analysis,
while legal literature often uses the term Causation Determination. Medicine analyzes
while law must make a determination. A medical causation analysis may provide
information critical to a legal causation determination. If this article were written for a
medical journal, it would be called “Causation Analysis in Occupational and
Environmental Medicine.” 3 This highlights the subtle, but important differences in
medical and legal terminology in these often complicated cases.
In the scientific arena, no causal hypothesis can be proven absolutely, no matter how
much evidence exists in its favor. 4 A thorough discussion of this statement is beyond the
scope of this article, however, it points out a critical problem in medicolegal practice, the
law looks to science to prove something, and scientists respond by stating that nothing is,
in fact, absolutely provable.
Causation in Medicine requires an Analysis; Law requires a Determination.
1
Margaret A Berger, The Supreme Court’s Trilogy on the Admissability of Expert Testimony. Reference
Manual on Scientific Evidence, Second Edition. Federal Judicial Center, West Group. 2000.
2
Tee L. Guidotti and Susan G. Rose, Science on the Witness Stand. OEM press. 2001.
3
Occupational Medicine is the medical specialty dealing with prevention and treatment of illness and
injury in workers, i.e., workers’ compensation cases. Environmental Medicine deals with prevention and
treatment of illness and injury caused by exposures in the non-work environment, i.e., toxic tort cases.
4
Philip Cole, The Hypothesis Generating Machine, 4 Epidemiology 271-73 (1993).
1
The Supreme Court, in Daubert v. Merrill Dow Pharmaceuticals, Inc. (1993, henceforth
called Daubert), noted that:
“there are important differences between the quest for truth in the courtroom and
the quest for truth in the laboratory. Scientific conclusions are subject to
perpetual revision. Law, on the other hand, must resolve disputes finally and
quickly” and that the Rules of Evidence were “designed not for the exhaustive
search for cosmic understanding but for the particularized resolution of legal
disputes.”
How then do scientists “prove” a cause and effect relationship?
Epidemiology is the Study of Disease within Human Populations.
An epidemiological study that seeks to establish a relationship between agent A (cause)
and disease D (effect) does not start by attempting to prove that exposure to agent A
causes disease D. Instead, a different hypothesis is made stating that exposure to agent A
does not cause disease D. This is called creating the null hypothesis.
The Null Hypothesis states that there is NO True Association
between an Agent and a Disease.
Scientists assume that there is no true association between an agent and a disease. Then
they merely disprove the null hypothesis. Disproving the null hypothesis increases the
probability that there is, indeed, a true association. Note that a double negative does not
absolutely prove a positive. Confusing? You bet.
Let’s restate this argument. In order to scientifically “prove” the theory that agent A
causes disease D, you must assume that agent A does not cause disease D, then find
evidence to disprove that agent A does not cause disease D. You assume a theory is
false, then you disprove the false theory. Thus, scientific proof of a theory depends on
the falsifiability of the null hyposthesis. To “prove” the above discussion is complicated,
assume the above discussion is not complicated. Reread the above two paragraphs. This
disproves (makes false) the statement that this discussion is not complicated.
Even Chief Justice Rehnquist, in his dissent in Daubert, which dealt with the
admissibility of scientific evidence, confirmed his confusion about this suspect scientific
process when he stated:
“I defer to no one in my confidence in federal judges; but I am at a loss to
know what is meant when it is said that the scientific status of a theory
depends on its “falsifiability,” and I suspect some of them will be, too.”
Is intimate knowledge of this confusing discussion of falsifiability of scientific theory
important to the lawyer who is trying to find a medical expert witness to make a medical
2
causation determination? No. What may be important is that the lawyer know enough
about this to ask a prospective medical expert witness these questions:



Can you produce published articles showing epidemiologic evidence that
exposure A could cause disease D?
What is the Null Hypothesis?
Does the published article adequately disprove the Null Hypothesis?
If your prospective expert witness, when asked the above questions, stares blankly back
at you without comment, “snows” you with illogical answers, or states only “I know
definitely that your client has disease D”, he or she may not be the ideal expert witness to
help you with medical causation determination.
In contrast, legal causation has two elements: Cause in fact and proximate cause. 5
Cause in fact is a necessary condition, and can be identified by a simple test: Would the
adverse outcome have been avoided “but for” the presence of the cause? Proximate
cause is the particular event or factor that initiated the chain of events leading to injury or
damage. Physicians, like a lay jury, may not understand the meaning of these legal
terms. If your prospective expert medical witness, when asked about cause in fact and
proximate cause, smiles and answers “I know all about them”, he or she may be a
professional expert witness trying to sound folksy.
Association v. Causation
Association is the statistical relationship between two or more variables or events. 6
Events are associated when they occur more or less frequently than would be expected by
chance. When an agent has no apparent effect on the presence or absence of a disease,
the agent and disease are considered to be not associated. When a disease occurs less
frequently than would be expected by chance, implying a preventive role for the agent (as
would occur with vaccination), the agent and disease as considered to have a negative
association.
Association is NOT Equivalent to Causation.
Many things are associated with each other, but do not have a causal relationship.
Smoking is associated with lower socio-economic status, however, smoking does not
cause lower socio-economic status. The presence of an association in no way implies
that an observed relationship is one of cause and effect. 7 One of the primary objectives
in epidemiology (remember, the study of disease in human populations) is to evaluate
whether an association between exposure and disease is causal.
A Goal of Epidemiology is to Prove or Disprove
5
Science on the Witness Stand.
Reference Guide on Epidemiology. Reference Manual on Scientific Evidence, second edition. Federal
Judicial Center, West Group. 2000.
7
Charles H. Hennekens, Julie E. Buring. Epidemiology in Medicine. Little, Brown, 1987.
6
3
Causal Association between an Agent and Disease.
Three questions come up when an epidemiologic study is used in legal disputes:
1. Do the results of the study show an association between an agent and disease?
2. What sources of error in the study could have caused inaccurate findings?
3. If an agent is associated with disease, is the relationship causal?
It doesn’t matter if an epidemiologic study presented in a legal dispute shows a positive,
negative, or no association, the opposing side will try to show there were errors in the
study which resulted in inaccurate findings, and that the study does not prove your point.
Error in Epidemiological Studies
The results of an epidemiologic study may reflect a true causal association between
exposure to an agent and development of a disease, however, it is possible that the
findings were erroneous. Problems with studies may be due to errors in design,
measurement, or interpretation. The main causes of study design error in epidemiologic
studies are:



Chance
Bias
Confounding
Error due to Chance
Findings in a study may be due simply to chance (called random variation). Since most
studies sample a portion of a population, random variation from sample to sample may
cause error. The larger the sample size, the larger the probability the sample represents
the whole population. The smaller the sample size, however, the larger the probability
that the sample does not represent the whole population, and thus the greater the
probability that findings are due to chance.
In medicine, a Case Report presents the clinical findings in one patient, usually with
some type of disease. An epidemiologic study, however, may present the findings of
hundreds or thousands of people with the same disease. A single case report that
suggests a causal association between an agent and a disease has a much great probability
of the association being due to chance than in a large epidemiologic study. Case reports
are very important in medicine, especially when evaluating a new disease, however,
because of the small sample size, there is a large probability that a possible association
between agent and disease is due to chance. Early AIDS case reports suggested an
association with AIDS, homosexual men, and the use of poppers (amyl nitrate, a
recreational drug). Early epidemiologic studies quickly revealed that use of poppers was
not causally associated with AIDS. Later epidemiologic studies revealed that
homosexuality is not causally associated with AIDS, but that unsafe sexual practices,
whether homosexual or heterosexual, and IV drug use with unclean needles was.
4
If a medical expert witness provides only a case or a few case reports that suggest a
casual association between exposure and disease, or states his or her causation
determination is based only on personal experience and opinion, there is a high
probability that the findings are due to chance and may be erroneous.
In Daubert, the Supreme Court found that a key question to be answered in determining
if a scientific theory “will assist the trier of fact will be whether it can be (and has been)
tested.” Case reports and physician’s opinions based only on personal experience can not
be tested. Additionally, Daubert noted “the courts should consider the known or
potential rate of error.”
How do you measure chance (a potential error in interpretation of findings) in a study?
The role of chance in a study is assessed by measuring statistical significance.
Statistical significance is usually measured with a P value, which is defined as the
probability that an observed effect in a study occurred by chance alone, given that there is
no true relationship between an agent and disease.
P Value = Probability that a study showed an agent
caused a disease, when no true causal association exists.
Scientists rather arbitrarily set a chance of 1 in 20 (5 percent, or 0.05) as the acceptable
level of error in most studies. 8 A P Value less than or equal to 0.05 is considered
statistically significant, that is, there is no more than a 1 in 20 probability that an
observed association between an agent and disease is due to chance. A P Value of
greater than 0.05 means that chance cannot be excluded as a likely explanation for the
observed association, and is not considered statistically significant.
P Value < or = 0.05, Statistically Significant (Results due to Chance < 5% of time)
P Value > 0.05, Not Statistically Significant (Results due to Chance > 5% of time)
If an acceptable level of chance in studies is set at 1 in 20, when you assess 100 different
studies, 5 of them may have significant findings due to chance alone. A prospective
medical expert who presents one study showing association between an agent and a
disease with statistical significance with a P Value of 0.05 may be presenting the 1 in 20
or so studies where the association is merely due to chance.
A confidence interval can also be used to assess statistical significance. A confidence
interval is a range of values calculated from the study results, within which the true value
8
The acceptance of chance in causal association varies with risk. Many people would buy a $100 lottery
ticket with a 1 in 10 chance of winning $1,000. Few people would get on an airplane that had a 1 in 1,000
chance of crashing. P Values can be set at different levels, such as 0.01 (1 in 10), or 0.01 or (1 in 100),
depending on the level of chance that would be acceptable in the study. But epidemiologic studies
normally set statistical significance at a P Value less than or equal to 0.05 (one in 20.)
5
is likely to fall, while the width of the interval indicates random error. It is usually
expressed as a percentage and an interval. A confidence interval gives more information
than just a P Value, and is usually expressed as a percentage (traditionally 95%) and an
interval. A 95% confidence interval means that if a study was repeated 100 times, the
true value would be in the interval 95/100 times. If this is confusing, don’t worry, here’s
what’s important to know:
A Confidence Interval that includes a Relative Risk of 1.0
(explained later) is Not Statistically Significant,
Results of the study May be due to Chance.
Error Due to Bias
Bias is systematic error in the design or conduct of a study. Selection bias occurs when
participants are selected for a study with bias (for example: someone at high risk of
developing a disease is selected over someone with low risk of developing a disease.)
Observation bias occurs when participants in a study are observed with bias, and occurs
when observers interpret information on participants differently (interviewer bias) or
subjects report events differently than they happened (recall bias.) Inaccuracies in the
collection of data are inevitable, and it is difficult or impossible to quantitatively measure
bias in an epidemiologic study. The inability to measure bias (producing study error) is
another reason that a scientific hypothesis can not be absolutely proven.
Error Due to Confounding
Confounding occurs in a study when an observed association (or lack of association) is
due to the mixing of effects between an agent, the disease, and a third factor that is
associated with the agent and independently affects the risk of developing the disease.
The important point is that confounding can lead to overestimation or underestimation of
the true association between an agent and disease.
Early studies showed an association between drinking coffee and mouth and throat
cancer. It was theorized that hot fluid somehow caused cellular damage resulting in
development of cancer. More thorough investigation showed that many coffee drinkers
also smoked cigarettes, and that most of the cancer found is these studies was attributable
to smoking. The coffee drinking studies were in error because of confounding due to
smoking.
Is intimate knowledge of the above causes of errors in epidemiologic studies important to
lawyers selecting expert medical witnesses? No. What may be important is that they ask
a prospective expert witness if the published and peer-reviewed articles he or she has
prove that exposure A causes disease D. If the answer is no, the prospective expert
witness does not have a strong case. If the answer is yes then ask these questions about
the articles:

How does chance, bias and confounding affect the study results?
6

Is the P Value in the study less than 0.05, or does the 95% Confidence
Interval in the study include a Relative Risk of 1.0?
If a prospective expert witness, when asked the above questions, stares blankly back, he
or she may not be the ideal expert witness to help with medical causation determination.
Burden of Proof v. Relative Risk
In most workers’ comp and toxic tort cases, the plaintiff bears the burden of proving both
causation-in-fact and proximate cause. Actually, the plaintiff must show that a casual
relationship more likely than not exits between an exposure and a disease. In civil cases,
the plaintiff’s burden of proof usually requires a “preponderance of evidence”, which
can also be defined as greater than 50% chance that the exposure resulted in the disease.
How do studies determine how strongly an agent is associated with a disease? Strength
of association is measured by different terms for different types of studies. Relative Risk,
Odds Ratio 9 , and Attributable Risk 10 are all measurements of strength of association in
studies.
Relative Risk (RR), grossly simplified, can be looked at as the number of cases of
disease in an exposed group divided by the numbers of cases of disease in an unexposed
group. 11
Relative Risk
=
# with disease with exposure
# with disease without exposure
If the Relative Risk is 1.0 (the # with disease with exposure is the same as the # with
disease without exposure) there is no association between exposure and disease. 12
For studies of smoking and lung cancer, the Relative Risk is about 10, which means
about 10 times more people develop lung cancer who smoke, compared to those who
develop lung cancer and don’t smoke.
A Relative Risk of 2.0 means twice as many cases of disease occurred in those exposed
compared to those unexposed, which implies (from the legal perspective) a 50%
likelihood that disease was caused by exposure. A relative risk greater than 2.0 would
9
Odds Ratio is used in a case-control study, and is a type of relative risk.
Attributable Risk is the amount of disease in exposed individuals that can be attributed to the exposure.
11
Relative Risk is actually the rate in the exposed divided by the rate in the unexposed. Incidence rate is
defined as the number of new cases of disease that develop during a specific period of time divided by the
number of persons in the study.
12
Relating back to statistical significance, if a Relative Risk of 1.0 is included in a Confidence Interval in a
study, it’s possible that there is no association between exposure and disease exits, and that an observed
association may be due to chance, and is not considered statistically significant.
10
7
imply that a plaintiff’s disease was more likely than not (greater than 50% chance) caused
by the exposure, and this has been interpreted as meeting the legal burden of proof. 13 , 14
Must you, the lawyer, understand the intricacies of Strength of Association measurements
in epidemiologic studies? No. What may be important is that you ask a prospective
expert witness:

Does the study you’re presenting, and which I’m basing my case on,
show a Relative Risk greater than 2.0, which would meet the burden
of proof in many civil courts?
PART TWO
Admissibility of Expert Testimony
Three recent Supreme Court decisions dealt with the admissibility of expert testimony. 15
The Daubert Decision
In 1993, the Supreme Court decided Daubert v. Merrell Dow Pharmaceuticals, Inc, a
toxic tort case where the petitioners, representing minor children born with serious birth
defects, alleged that the defects had been caused by the mother’s ingestion of Bendectin,
an antinausea drug.
The petitioners presented eight experts who concluded that Bendectin can cause birth
defects. Their conclusions were based on “in vitro” (test tube) and “in vivo” (live)
animal studies, pharmacological studies showing structural similarities between
Bendectin and other substances known to cause birth defects, and “reanalysis” of
previously published epidemiological (human statistical) studies. The respondant’s
medical expert , however, had reviewed more than 30 published studies involving over
130,000 patients, and noted that not one published study in human beings had found
Bendectin to cause birth defects.
The District Court granted the respondant’s motion for summary judgement, noting that
given the vast amount of epidemiological data concerning Bendectin, expert opinion
which is not based on epidemiological (human) evidence is not admissible to establish
causation. In vitro cell studies, animal studies, and chemical structure analysis alone can
not establish causation in humans. The petitioner’s “reanalysis” of previously published
studies (that found no causal like between Bendectin and birth defects) were ruled in
13
“The use of scientifically reliable epidemiological studies and the requirements of more than a doubling
of the risk strikes a balance between the needs of our legal system and the limits of science.” Merrell Dow
Pharms., Inc. v. Havner, 953 S.W.2d 706, 718 (Tex. 1997.)
14
Relative risk greater than 2.0 “support[s] an inference that the exposure was the probable cause of the
disease in a specific member of the exposed population.” Landrigan v. Celotex Corp., 605 A.2d 1079, 1087
(N.J. 1992.)
15
Margaret A. Berger, The Supreme Court’s Trilogy on the Admissibility of Expert Testimony. Reference
on Scientific Evidence, Second Edition. Federal Judicial Center, West Group. 2000.
8
admissible because they had not been published or subjected to peer review. The Court
of Appeals also rejected the petitioner’s reanalyses as they were “unpublished, not
subjected to the normal peer review process and generated solely for use in litigation.”
The Supreme Court noted that a key question to be answered is whether a scientific
theory can and has been tested. “Scientific methodology today is based on generating
hypotheses and testing them to see if they can be falsified; indeed, this methodology is
what distinguishes science from other fields of human inquiry” 16 Simply put, the status
of a scientific theory is based on its testability (as determined by its falsifiability, which,
of course, is not so simply put.)
The Supreme Court also noted that another pertinent consideration is whether the theory
has been subjected to peer review and has been published. They commented, however,
that peer review and publication does not necessarily correlate with reliability, and that
some new and innovative theories will not have been published. Additionally,
consideration should be given to the known or potential error rates and standards
controlling the scientific technique’s operation.
In summary, the Daubert decision notes that the court should consider admissibility of a
scientific theory based, non-exclusively, on these four factors:
Testibility
Peer review and publication
Potential rate of error
Standards for controlling operation
Prior to Daubert, many courts used the “general acceptance” test, which was based on the
so-called Frye test. The Frye test originated in a 1923 decision dealing with the
admissibility of evidence based upon a systolic blood pressure deception test, a crude liedetector test. Because the deception test had not gained standing and recognition (general
acceptance) by scientific authorities, evidence from the test’s results was ruled
inadmissible. For many years, the Fry “general acceptance” test was the exclusive test
for admitting expert scientific testimony. However, the Frye test was considered to be
superseded by the Federal Rules of Evidence, which was enacted by Congress in 1975.
In Daubert, the Supreme Court agreed that Frye had been superceded by adoption of the
Federal Rules of Evidence (general acceptance was not the exclusive admissibility test),
however, they also noted that “general acceptance” of a scientific theory can yet have a
bearing on an inquiry.
Another of the important themes in Daubert is that the trial court is the “gatekeeper” and
should act to screen proffered expertise, ensuring that what is admitted “is not only
relevant, but reliable.” The majority opinion in Daubert noted that the court has not only
the power, but the obligation to be a gatekeeper. Thus courts should look seriously at the
above-mentioned four factors when considering the admissibility of scientific evidence.
If these non-exclusive criteria are not adequately met, the court, acting as a “gatekeeper”
16
Green 645
9
can refuse to admit the evidence. The Daubert majority opinion closing summary noted
that “general acceptaince” is not a necessary precondition to the admissibility of scientific
evidence, that the trial judge is assigned the task of ensuring that an expert’s testimony
both rests on a reliable foundation and is relevant to the task at hand, and that pertinent
evidence based on scientifically valid principles will satisfy those demands. The
judgment of the Court of Appeals was vacated, and the case was remanded for further
proceedings consistent with the opinion.
The Joiner Decision
In 1997, the Supreme Court decided General Electric Co. v. Joiner, a toxic tort case
where the petitioner was a long-time smoker with a family history of lung cancer and
claimed his exposures to polychlorinated biphenyls (PCBs) had promoted his
development of lung cancer. Even though there were four epidemiological studies
presented, the trial court found these studies insufficient, and applied the Daubert criteria,
excluded the plaintiff’s expert’s opinions, and granted the defendant’s motion for
summary judgment. The court of appeals reversed the decision because “the Federal
Rules of Evidence governing expert testimony display a preference for admissibility”.
The Supreme Court examined the record, determined that the plaintiff’s experts had been
properly excluded because the studies relied upon were not sufficient to support the
conclusion that Joiner’s PCB exposure contributed to his cancer, then reversed the
decision without remanding the case. The Court concluded that the plaintiff’s expert’s
causation opinions were merely speculation, and that it was never explained how the
experts extrapolated their opinions from animal studies to the plaintiff’s (human)
exposure. The Joiner decision noted that a court may conclude that there is simply too
great an analytical gap between the data and the opinion proferred.
The Joiner decision reinforced Daubert by again noting that the trial court should act as
the “gatekeeper” in determining admissibility of scientific evidence.
The Kumho Decision
In 1999, the Supreme Court decided Kumho Tire v. Carmichael, a non-toxic tort case, in
which plaintiffs brought suit after a tire blew out on a minivan, resulting in the death of
one person and serious injuries to others. The plaintiff’s expert witness, an expert in tirefailure analysis, concluded by visual analysis that the blowout was caused by defective
tire manufacture or design. There was no evidence presented that other experts, papers,
or articles supported the tire-failure expert’s theory. The district court concluded that the
Daubert gatekeeping obligation applied to both scientific knowledge and technical
analysis. The district court held that the tire-failure expert’s methodology did not meet
the Daubert criteria, excluded the expert’s testimony, and granted the defendant’s motion
for summary judgment.
The court of appeals reversed the decision stating that Daubert applies only to scientific
testimony. The Supreme Court held that the trial court’s gatekeeping obligation applies
10
not only to testimony based on “scientific” knowledge, but extends also to testimony
based on “technical” and “other specialized” knowledge. Simply put, the Court stated
that a court’s gatekeeping obligation extends to all expert testimony. The Court
concluded that the trial court had not abused its discretion when excluding the tire-failure
expert’s testimony, and reversed the opinion of the appeals court, thus allowing the
exclusion of the expert witness.
Justice Breyer’s Kumho opinion states that “we can neither rule out, nor rule in, for all
cases and for all time the applicability of the factors mentioned in Daubert, nor can we
now do so for subsets of cases categorized by category of expert or by kind of evidence.
Too much depend upon the particular circumstances of the particular case at issue.” In
Kumho, the Court found that the Daubert factors may bear on a judge’s gatekeeping
determinations, and that these factors “may or may not be pertinent”, depending “on the
nature of the issue, the expert’s particular expertise, and the subject of his testimony.”
The Kumho decision extended the trial judge’s gatekeeping obligation related to expert
testimony as first discussed in Daubert, to include all expert testimony, and endorsed a
flexible, non-doctrinaire approach that requires district courts to focus upon the particular
circumstances of a case. Kumho did not say the Daubert factors are irrelevant, but that
they may or may not be pertinent.
Daubert, Joiner, and Kumho, have helped clarify the admissibility of expert testimony,
however, battles over admissibility will continue, particularly related to toxic tort cases.
PART THREE
Finding an Expert Witness who can make an Appropriate Medical Causation
Determination
Most physicians have no training in and little understanding of medical causation
determination. Medical school teaches physicians mainly to diagnose and treat.
Causation may be discussed in terms of infectious disease; ie, this bacteria causes this
disease. Med students may learn about Koch’s postulates, criteria developed in the midnineteenth century to help determine the cause of an infectious disease.
In order to “prove” an organism causes disease using Koch’s postulates, these criteria
must be met: 17
1. The organism must be found in all cases of the disease.
2. The organism must be isolated from patients with the disease and grown in
culture.
3. The cultured organism must produce the disease when inoculated into a
susceptible host.
17
Science on the Witness Stand.
11
Alas, though Koch’s postulates work well for microbiological organisms that cause a
single disease, they are useless in most workers’ compensation or toxic tort cases, where
the agent of concern may be a chemical or other non-organism exposure (like heat,
radiation, noise, or cumulative trauma.) Let’s restate this:
The infectious disease model of causation taught in medical school is useless in most
workers’ compensation or toxic tort cases. 18
Most residency trained and specialty board certified physicians have no training in and
little understanding of medical causation determination. 19 In general, practicing
surgeons, be they orthopedic surgeons, neurosurgeons, or ophthalmologists, are not
terribly concerned with causation. They diagnose, then treat a problem (often with
surgery.) The diagnosis of a type of tumor, and the removal of that tumor is not
dependent on the surgeon making an appropriate medical causation determination.
With the exception of infectious disease, most practicing physicians (internists,
emergency room, family practice, obstetrician/gynecologist, etc) are not terribly
concerned with causation. Determining the cause of an acute myocardial infarction (MI,
or heart attack) is not a high priority for ER docs, they’re busy trying to diagnose and
treat the problem. Determining that a patient’s morbid obesity is more likely than not to
be the cause of an MI is not that important while acutely treating the MI. 20
With infectious diseases, determining the agent of causation is important in order to
identify the bacteria or virus, so the patient can be treated with the appropriate antibiotic
or antiviral. You treat with antibiotics in order to prevent further infection.
This brings up a major point, in medicine:
Determining Causation is Important in order to Prevent Illness or Injury
In order to prevent an illness or injury, you must know what caused the illness or injury.
Prevention is thus directly linked to causation. Most practicing physicians do not have
the training, knowledge, or time to discuss prevention with their patients, they are, again,
busy diagnosing and treating. However, there is a medical specialty that deals with
preventing illness and injuries, it’s called Preventive Medicine.
18
Infectious disease is important in some workers’ compensation or toxic tort cases, examples being workrelated HIV or hepatitis infection, Legionnaire’s disease, or tuberculosis. However, doctors do not now
normally inject these organisms into susceptible humans to prove causation. Because HIV infection has
not met all of Koch’s criteria (it’s unethical to inject HIV into a susceptible individual) there are still some
people who do not believe that HIV causes AIDS.
19
The exception being physicians residency trained in Preventive Medicine.
20
Multiple factors, such as obesity, hypertension, elevated cholesterol, diabetes, family history, smoking,
lack of exercise, etc., increase risk for having an MI. ER docs, while evaluating a patient with an acute MI,
have more important things to do than determine causation, they are diagnosing and treating the problem
and trying to save a life.
12
Preventive Medicine seeks to Prevent Illness and Injuries in Humans
The American Board of Preventive Medicine recognizes three specialties: General
Preventive Medicine, Aerospace Medicine, and Occupational and Environmental
Medicine.
General Preventive Medicine deals mainly with public health, preventing
and treating sexually transmitted diseases, tuberculosis, lung cancer from
smoking, etc., in the general population.
Aerospace Medicine deals with preventing and treating problems caused
by the effects of flying and high altitude on pilots and aircrew.
Occupational and Environmental Medicine deals with preventing and
treating illness and injury caused by the workplace or exposures in the
general environment.
Since all workers’ compensation cases deal with the workplace, and most toxic tort cases
deal with exposures related to the workplace or general environment, Occupational and
Environmental Medicine physicians are the specialists most appropriate for overall
evaluation of these cases. Unfortunately, there are relatively few trained and board
certified Occupational and Environmental medicine physicians in the United States. 21
There are so few Occupational and Environmental Medicine physicians practicing in this
country that most judges, arbitrators, jurors, lawyers, lay people, in fact, probably most
nurses and physicians do not know this medical specialty exists. 22
So Whom to Use as an Expert Witness?
Consider contacting a respected23 physician in the medical specialty that deals with the
diagnosis and treatment of the disease or injury of concern. If the case is about a
21
There are currently less than 25 Occupational and Environmental Medicine (OEM) residencies in the
United States, and most of these have only between 1 and 4 residents per year, resulting in only about 60
new OEM physicians graduating per year. There are many more physicians who are board certified in
OEM, who have not had formal residency training, but who became board certified based on experience
and testing. However, the vast majority of work-related injuries are treated by primary care physicians
(family practice or ER) that have no formal training or certification in OEM. These often very skilled
providers of work-related injury care may have little knowledge of or no training in preventive medicine or
causation determination.
22
Employers and workers will certainly know there are doctors treating workers’ compensation cases
(often called the “company” doctor, since in many states, the company can direct care to specific providers)
but will not know that there is residency training in this area.
23
Respect may be based on training, experience, position, such as chairman of a department or head of a
residency, or on publication of papers on the specific topic, etc. In almost all cases, you’ll want someone
who is residency trained and board certified in their specialty. It doesn’t look good when an opposing
attorney grills your expert witness and finds out they are not residency trained nor board certified. This is
another reason why Occupational and Environmental Medicine physicians aren’t used as expert witnesses
often, as the majority of physicians practicing this specialty are not residency trained nor board certified,
and would no be considered qualified by a judge to be an expert.
13
miscarriage thought due to a chemical exposure, contact an obstetrician/gynecologist. If
it’s about asthma contact a pulmonologist or allergist. If it’s about possible carpal
tunnel contact a hand surgeon. 24 If it’s about leukemia contact an oncologist, etc.
This respected medical specialist should confirm the correct diagnosis and treatment in
the patient. If the diagnosis or treatment is found to be in error, there may be grounds for
a malpractice case. If the diagnosis is confirmed and the treatment is found to be
appropriate, you must request a medical causation determination.
Hire a Physician Specialist to evaluate Diagnosis and Treatment
The million dollar question is, “Was the disease or injury caused by exposure in the
workplace or environment?” 25 Often the whole case rests upon answering this question.
But be warned, you’ve hired someone who has nothing to lose if they incorrectly attribute
a specific disease to specific agent or exposure. A physician will not lose his or her
medical license for making an erroneous causation determination. Causation
determination is not diagnosing or treating. Causation determination is not considered
practicing medicine, therefore there can be no medical malpractice.
There is No Malpractice for Faulty Causation Determination
So the high priced respected medical specialist you’ve hired has little personally to lose if
they falsely state exposure to an agent caused a disease or injury. The will not lose their
medical license, their malpractice insurance will not go up, they will not get reprimanded
by the state medical society. In workers’ compensation cases, stating the illness or injury
was caused by exposure at work may result in quicker and higher medical
reimbursement. Alas, since no causal hypothesis can be proven absolutely, it’s
impossible to absolutely prove exposure to an agent is safe, or absolutely prove exposure
to an agent is dangerous, and really no way to “prove” that an expert’s causation
determination is faulty.
You may have spent many months, and tens of thousands of dollars preparing a workers’
compensation or toxic tort case, hired the most respected medical specialist in the area
who has stated exposure to agent A caused disease D, and your expert witness testimony
may be ruled inadmissible. How do you avoid this?
Back to part one, ask your respected medical specialist to answer the question:
1. Can you produce published articles showing epidemiologic evidence that
exposure A could cause disease D?
24
Many primary care providers misdiagnose carpal tunnel syndrome, considering any wrist area tendonitis
as carpal tunnel syndrome.
25
Actually, it’s often the multi-million dollar question. Toxic tort cases are often settled for tens of
millions of dollars.
14
If your respected medical specialist can not provide a single published epidemiologic
article 26 showing evidence that exposure A could cause disease D, chances are this
specialist’s testimony would not be considered admissible.
If an appropriate published article is presented showing evidence that exposure A could
cause disease D, then ask the specialist the remaining 6 questions from part 1 about the
article, beginning with “What is the Null Hypothesis?” Asking these questions fulfills
much of the criteria for admissibility set forth in Daubert, including testability, peer
review and publication, potential rate of error, and general acceptance.
Besides contacting a prospective medical expert witness in the specialty related to the
illness (ie, oncology, obstetrics, surgery), I’d encourage you to consider another option.
Consider hiring an experienced Occupational and Environmental Medicine physician 27 to
review the appropriate textbooks and articles and make a causation determination as to
whether or not a specific illness is possibly caused by a specific agent.
Hire an Occupational and Environmental Medicine Physician
to make a Causation Determination
Experienced Occupational and Environmental Medicine physicians may not be experts in
diagnosing and treating a specific illness, however, they are experts in causation
determination (remember it’s a preventive specialty, you can’t prevent something unless
you understand what causes it.) Your physician specialist will be an expert in diagnosis
and treatment, but may not be an expert in caution determination (excluding infectious
disease, you can expertly diagnose and treat something without knowing what caused
it.) 28
I was motivated to write this article because I have consulted on numerous cases where,
unfortunately, lawyers had hired expert witnesses who had made faulty causation
determinations. These poor 29 lawyers were totally flustered when my evaluation and
report showed that, contrary to their other specialty expert’s opinion, there were
26
A single case report published in a medical journal does not establish causation, it may not even establish
association, a case report is merely the presentation of a case. However, if the case report presents a new
disease, or a possible new cause of a disease, care reports may be very valuable. Because a new
hypothesis, which may be presented for the first time in a case report, may not be peer reviewed or testable,
the Supreme Court, in Daubert, recognizes “that, in practice, a gatekeeping role for the judge, no matter
how flexible, inevitably on occasion will prevent the jury from learning of authentic insights and
innovations.” The Court thus acknowledges that recently discovered diseases or new causation theories
may in fact be real, but will not meet the admissibility criteria set forth in Daubert.
27
Being somewhat biased, I’d recommend contacting a physician that is residency trained and board
certified in OEM, however, someone that’s not residency trained but board certified, or simply experienced
in OEM may suffice. In a legal situation, it would be almost unthinkable to contact a surgeon or
obstetrician who was not both residency trained and board certified in their specialty to give medical
advice.
28
Actually, we don’t know the cause of most tumors and cancers.
29
Poor meaning both unfortunate and not wealthy. They’d spent thousands of dollars to get medical expert
opinions that were, quite frankly, wrong.
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absolutely no testable, peer reviewed and published studies that “proved” or “disproved”,
or general acceptance that agent A caused disease D in their client.
Based on my experience, I’d recommend any lawyer to consult with an experienced
Occupational and Environmental Medicine physician before taking on a complicated
workers’ compensation or toxic tort case. If there’s no evidence to support causation, it
doesn’t really matter what high-priced medical specialist you hire to confirm diagnosis or
treatment, their opinion on causation may be faulty, resulting in a judge, acting as a
“gatekeeper”, ruling your expert testimony inadmissible.
It may take an experienced Occupational and Environmental Medicine physician only a
couple hours to review a case, review the published literature, and make an initial
causation determination. Some physicians take between one to four hours to initially
review a case and literature then make a verbal report. A verbal report is then made so
that the initial opinion is not discoverable in court. Often these initial opinions do not
support the stance the lawyer who hired the expert witness desires, and by giving a verbal
report, this contradictory information is not available to be included in the record. If the
initial verbal report supports the stance the lawyer desires, then a formal written report
may be requested, which may take a few or many hours depending on the complexity of
the case. 30
Non-Physician Expert Witnesses
There are three other groups of non-physicians that are frequently used as expert
witnesses in workers’ compensation and toxic tort cases and may be involved in
causation determination; toxicologists, epidemiologists, and industrial hygienists. 31
Toxicology is the study of poisons (toxins) and their effects on organisms. Toxicologists
usually do studies (experiments) at the cellular level, or with animals. Rarely do
toxicological studies directly involve humans, since it’s relatively unethical to willingly
expose humans to a known or suspected poison. 32 Results of toxicological studies done
at the cellular level or in animals, must then be extrapolated to humans. Studies done
involving animals often use high-dose exposure to toxins, which maybe irrelevant and
unreliable when extrapolated down to low-dose exposures in humans. The District Court,
in Daubert, stated that “expert opinion which is not based on epidemiological evidence is
not admissible to establish causation. Thus, the animal-cell studies, live-animal studies,
and chemical-structure analyses on which petitioners had relied could not raise by
themselves a reasonably disputable jury issue regarding causation.” Toxicologic studies,
by themselves and without epidemiologic support, do not establish caution.
30
This written report may cost a few hundred or a few thousand dollars, but whether it supports or does not
support the case, it may save hundreds of thousands of dollars in further legal costs, or result in millions of
dollars in judgments.
31
Toxicologists and epidemiologists are often also physicians. However, they are frequently non-physician
PhDs. Industrial hygienists are rarely also physicians.
32
Toxicological studies directly involving humans mainly involve medicinal drugs.
16
If no studies in human beings support the findings, testimony of a toxicologist may
be consider not admissible.
Epidemiologists study the relationship between agents and disease in humans, and are
frequently used as expert witnesses, however, you can count on the opposing side trying
to discount specific studies due to error caused by chance, bias, or confounding. The big
problem with using epidemiologists as expert witness is that epidemiologic studies look
at disease in human populations. Any result from a population must be extrapolated
down to an individual. Epidemiologic studies certainly confirm that the relative risk of
getting lung cancer is 10 times higher for smokers compaired to non-smokers, but these
studies can not predict if you’ll get lung cancer, or if you have lung cancer, absolutely
confirm that you got lung cancer from smoking. Even if an epidemiologic study showed
a relative risk of 2.0 of getting some disease after some exposure, maybe 45% of people
with the disease did not have exposure. Imagine making a faulty causation determination
45% of the time, it could happen that often when results of a group study are extrapolated
down to an individual.
Epidemiologist who present studies that are not testable, peer-reviewed and
published, or that do not have “general acceptance”, may be considered not
admissible.
Industrial Hygienists measure the presence and level of substances, such as chemicals,
radiation, noise, mold, dust, or fumes, etc. You may hire the top medical specialist in the
country that confirms the diagnosis and treatment of disease D your client. You may hire
the top Occupational and Environmental medicine physician in the country that confirms
that agent A can cause Disease D in your client. But if you can not prove that agent A
was present, and your client was, indeed, exposed to agent A, there is no case. Disease D
can not be caused by Agent A if Agent A was not present. A discussion of error in
industrial hygiene sampling and reporting is beyond the scope of this article, however, if
a certified industrial hygienist (CIH) was used there’s a good chance there is no
significant error in sampling.
There are four question to be answered when evaluating an occupational or
environmental exposure:
1. Is the agent present?
2. Is there a route of exposure for the agent (air, dust, water, food)?
3. Did the agent get into or on the body?
4. If in the body, did the agent cause effects?
Industrial hygienists can answer questions 1 and 2. Physicians can answer questions 3
and 4. If question 1 or 2 are negative, questions 3 and 4 are not relevant. If there is no
agent present, or no route of exposure for an agent to get into the body, the agent can not
have caused a disease. If an industrial hygienist finds that there is no agent present, or
there is no route of exposure for the agent, medical expert testimony is irrelevant.
If there is no agent present, or no route of exposure,
17
there is no causation.
For example, asbestos is present in many buildings in the United States. Samples from
insulation or walls confirms the presence of asbestos. If the insulation or walls are in
good shape (the asbestos is encapsulated) there may be no asbestos present in air
sampling or dust sampling. If air and dust sampling is negative, there is no route of
exposure for asbestos to get into or on a human body, and there is no risk of asbestosrelated disease from working in or living in the area. However, if the insulation or walls
are damaged (friable), asbestos may be present in the air or dust, which could be inhaled
or swallowed resulting in asbestos-related disease (mesothelioma or asbestosis.) In this
case the agent is present, and there are routes of transmission (air and dust.)
Unfortunately, many workers’ compensation or toxic tort cases move forward without
documenting the presence of the agent of concern and the route of exposure.
An Industrial Hygienist should Investigate the Presence
of an Agent and the Route of Exposure.
Closing
Causation determination is critical in both workers’ compensation and toxic tort cases.
Causation is not the same as association.
Medical and legal definitions of causation are different, which has created problems with
medical expert testimony in the courts.
Three recent Supreme Court decisions addressing the admissibility of expert witnesses
and studies dealing with medical causation determination, have shed some light on the
subject, but left some questions unresolved.
The testimony of toxicologist’s may be not admissible if the experiments are not
supported by human studies.
The testimony of epidemiologists or physician experts that is based on studies that are not
testable, peer reviewed and published, or of “general acceptance” in the medical
community, may be not admissible.
Industrial hygienist should be used to confirm the presence of an agent and the route of
transmission. If neither of these are confirmed, there is no causation.
Physician specialists are usually used as expert witnesses to determine diagnosis and
treatment, however, they may not be the best expert for causation determination, which
may be best analyzed by an Occupational and Environmental Physician trained in
Preventive Medicine.
18
Special thanks to James Brown, Esq.
Jon T. O’Neal, MD, MPH, received his MD from the University of Kansas School of
Medicine, and completed a residency in Occupational and Environmental Medicine and a
Masters of Public Health at Harvard. He is board certified in Occupational and
Environmental medicine, and is a Fellow in the American College of Occupational and
Environmental Medicine.
flydocfly@aol.com
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