Medical Review and Causation

Dr. Guidotti regularly reviews medical records and conducts independent medical evaluations. He conducts disability evaluations and particularly evaluations to establish probable causation and to clarify complicated medical issues.

Dr. Guidotti’s core expertise is in occupational and environmental medicine, especially lung disease and toxicology. Over the years Dr. Guidotti has developed special expertise in certain specific areas that arise occasionally in litigation, such as the oil and gas industry, health issues of firefighters and related occupations, and hydrogen sulfide.

Dr, Guidotti has deep health expertise in many other sectors, occupations, and environmental issues, beyond the special areas mentioned above. He has demonstrable qualifications and experience in health, safety, environment, sustainability, occupational health, occupational and environmental medicine, environmental health, air pollution, inhalation toxicology, occupational lung disease, chemical hazards, public health, risk science, risk communication, and ecosystem health. For that reason, clients often use him to “connect the dots” in difficult cases requiring integration of these fields to get the big picture.

Causation: A Personal View

Causation, as normally used in occupational medicine and related fields, is the determination of the probable cause of the subject’s condition or disability. (A subject may be a plaintiff, claimant, injured worker, or subject of monitoring, but is not necessarily a patient, for example in an independent medical evaluation.) In workers’ compensation, causation not only means identifying the factor that created the condition but demonstrating that it arose out of work.

Causation is not the same as diagnosis, although the two are related. The assessment of causation in occupational medicine is primarily in order to establish the association with work, not to guide treatment. Causation is more central even than diagnosis in initiating compensation and stimulating prevention. It is common to be able to make a diagnosis without knowing the cause. It is usually, but not always, necessarily to know the exact diagnosis to assess causation, as long as the pathological process is known. For example, one can know that a worker has nonallergic airways reactivity following an exposure clearly associated with work without determining for certain whether it is occupational asthma associated with irritant exposure, reactive airways dysfunction syndrome or aggravation of pre-existing but subclinical airways reactivity in allergic rhinitis.

For the expert specializing in chemical tort litigation and addressing general causation, it is essential to have a sound working knowledge of both epidemiology and toxicology. Epidemiology shows patterns of disease and what happens in human populations. Toxicology explains why the effect happened and predicts when. However, both are limited in their role to general causation. To deal effectively with individual cases and to be able to apply this knowledge to specific causation, it is critical to have strength in clinical medicine.

Non-physician epidemiologists routinely qualify as experts in “general causation” (providing evidence for the capacity of an exposure or hazard to cause a disease; for example, that a certain chemical is carcinogenic to people) but their qualification and scope of expertise is usually limited by the court. A Ph.D. epidemiologist can inform the proceedings (very effectively) and describe the population-based science but cannot take the last, crucial step of applying the science to the specifics of a particular case. In many respects, the role of the physician expert has therefore actually grown stronger in recent years.

Epidemiology and Toxicology Inform General Causation

Epidemiology can inform the court with a description of what happens most of the time or what is most probable, but the interpretation still must be brought to the level of the individual case. This may mean demonstrating that the plaintiff or claimant is similar to a group at demonstrably high risk or that he or she is different and therefore belongs to a subgroup or has unique characteristics and so their risk is not adequately described by summary statistics. This is where a well-prepared, knowledgeable medical expert can play a critical role.

Epidemiology is fundamentally a science of generalizations. The basic approach of epidemiology to estimating risk is to measure the experience of a population of individuals with the expectation that, all other things being equal, the overall risk for the group will be a valid estimate for most members of the group. Epidemiology has become increasingly valued in health-related cases precisely because it is a powerful tool for generalization.

However, epidemiology has limitations precisely because it is a science of generalizations. That is its great strength but also its great weakness. When applied to class action litigation, generalizations make sense because one is considering patterns in a large population. However, most litigation involves individual plaintiffs and the individual circumstances of each case must be separately considered. This is also true in most adjudication systems, such as workers’ compensation.

In the assumptions underlying conventional inferential statistics, the risk reflected by the group experience is an estimate for a hypothetical set of similar groups under similar circumstances, not necessarily an accurate prediction for an individual member of the group. It is only the best estimate for a member of that group. This estimate may be misleading if there is considerable variation or heterogeneity in the population. Epidemiologists know this and are generally careful in their testimony to describe patterns in populations rather than conclusions about individuals.

Another science of importance in toxic torts and occupational disease cases is toxicology, although its role seems to have faded since mid-20th century. Clinical toxicology is often difficult as the basis for an expert opinion because much of it is based, necessarily, on case reports and small case series, and therefore cannot be analyzed like epidemiological studies. Research toxicology is even more difficult because issues of extrapolation to human beings and threshold dose invariably limit the generalization of scientific findings. In general, and there are many exceptions, toxicological studies are most useful to the expert in three situations:

1) to explain the mechanism behind an association (such as disease causation) found in an epidemiological study,

2) in the case of research toxicology, to demonstrate what might happen in the human being, and

3) to demonstrate what does happen in well-documented cases of clinical toxicity which, taken together, show a pattern.

Clinical Medicine Informs Specific Causation

Although medical opinions are no longer accepted without a requirement to show the evidence, once the evidence is presented in court it takes a physician to take the expert testimony the rest of the way, to show how the general science applies to the individual case. However, physicians and sometimes nurses are accepted as more authoritative on matters of treatment and individual or “specific causation”. The physician expert may be called upon to render narrowly medical expert testimony and opinion, but the most fundamental role of the physician expert today is to bring the generalizations down to apply to the individual case.

The approach to medical evaluation in occupational disease preserves the traditional orientation of identification, diagnosis, functional evaluation, treatment, and prognosis but requires further information depending on the case and the criteria of the agency handling compensation or liability:

• level of causation (direct, proximate, precipitating, underlying)
• work relationship,
• apportionment,
• explanation of the causal circumstances,
• assessment of impairment,
• prediction of future impairment,
• surveillance for sentinel event monitoring.

Daubert: A Key Decision

In the United States, one critical court decision clarified the standard for applying scientific information to dispute resolution. The decision in Daubert v. Merrell Dow Pharmaceuticals, Inc. 113 S. Ct. 2786 (1993) attempted to set a new and higher standard for federal courts in reviewing scientific evidence. This federal court decision was later expanded upon and served as the model for many state decisions. (This was a decision incidental to a civil case regarding the Bendectin®, which was a drug for morning sickness that was alleged to cause birth defects. Although there is no evidence that Bendectin® actually had this effect, it was withdrawn from the market because of the expense of litigation and future liability.)

The effect of this decision was that judges presiding over technically complicated cases have assumed a new “gatekeeping” function, monitoring scientific evidence that they cannot be expected to have mastered. In keeping with an earlier trend in some state high courts and in general trends in adjudication bodies, Daubert (pronounced “DOW-bert”) requires federal courts to examine the quality and logic of scientific testimony in arriving at their decisions and to apply the standards of science to scientific testimony. Its influence has been felt throughout the legal system, resulting in higher expectations for rigor and persuasiveness in the opinions offered by expert witnesses. A consequence of this case has been that it is also much harder to demonstrate sufficient evidence to support a “first case” when a hazard is new or an association has not previously been recognized.

The Daubert decision imposed a great burden on courts. Few judges and clerks are prepared to assess scientific data independently. In the rare instance in which a judge has had access to a consultant capable of rendering an independent assessment, there have been concerns that the in-house expert could unduly affect the decision by manipulating the assessment and by inadvertently supplanting the role of the judge.

Courts after Daubert have required more documentation of the evidence and have set a higher standard. Peer-review is now the accepted legal standard and experts are often asked on the stand if the evidence they cite and the opinions, or theory of the case, they espouse have been peer reviewed. Theories that are specific to a particular case have no opportunity to be peer reviewed.

Since Daubert, courts also have put much greater emphasis on defensible arguments based on empirical data and less emphasis on expert judgment. The ability to base testimony on evidence, and to fit the evidence together in an objective-appearing way, is far more important in today’s courtroom. Opinion is not enough.

There is nothing unethical about holding one opinion with respect to the legal interpretation of a set of findings and another with respect to the scientific interpretation, because the standards of certainty are hugely different. One may legitimately consider a matter to be very likely but not scientifically proven (such as asbestos as a cause of colon cancer). Often, the scientific evidence for an association is strong but not conclusive. In such cases, it is entirely reasonable and responsible, although frequently uncomfortable, for an expert witness to maintain on the witness stand that there is or is not an association, on the basis of an interpretation of “the weight of evidence”, but to maintain in a scientific forum that the association is not proven because it has not been proven beyond a reasonable doubt. What counts in the end in a legal case is the weight of what evidence exists.

Standard of Certainty

Health and medical knowledge are essential to the resolution of occupational health-related disputes in law (such as third-party tort litigation against the manufacturers of allegedly unsafe products) and administrative adjudication (such as workers’ compensation). How to use this knowledge is not always clear. Here, medical training, with its tolerance for and understanding of diagnostic uncertainty, provides a better preparation for the expert than training purely in science.

The central concept in the rendering an opinion is the standard of certainty”. (See also Chapter 25.) Scientists know how to evaluate evidence in science and have internalized the “95% certainty” principle for statistical significance inherent in experiments and studies, as embodied in the standard formulation “p < 0.05”. This rigorous standard is not unlike the standard of persuasion that is applied in criminal law, which in the American and Canadian legal systems is “beyond reasonable doubt”. However, civil law to resolve disputes between parties (and most systems of adjudication) has a different and very practical standard: the balance of probabilities, or “weight of evidence”, which translates to >50% certainty.

The critical issue facing the expert is only rarely to supply a key fact or missing link in a chain of evidence. Much more often, the challenge is how to evaluate and apply scientific evidence when the standard is “more likely than not” rather than scientific certainty. In other words, what would be the conclusion of epidemiology and the biomedical sciences based on available data if the standard of certainty were 50% rather than 95% certainty?

A good example is the association between either colon cancer or cancer of the larynx and exposure to asbestos. The weight of evidence in the literature on either strongly suggests that there is an association and both toxicology and logic (since asbestos causes the same tissue type of cancer in the lung) suggest that it is causal. The principles of scientific inference, however, do not confirm that this association is consistent, statistically significant, or strong enough to be sure that the association is causal. In this situation, it would be perfectly valid for the expert to take the opinion that asbestos caused the cancer (all other things being equal) and equally valid for the same expert, speaking as a pure scientist at a scientific meeting, to take the position that asbestos has not been proven to cause the disease.

Some medical expert witnesses with a scientific background stick to the familiar rules of science and are therefore, by definition, too conservative in their opinion. Others may feel liberated by the looser standard of civil litigation and free to make up theories and opinions that extrapolate far beyond solid evidence. The adversarial structure of the legal system encourages extreme interpretations. Litigation has therefore been a spawning ground for junk science, which has threatened the credibility of experts in general and has probably discouraged many knowledgeable investigators and practitioners from sharing their knowledge when it has been needed.