When presenting causation in the courtroom it is first important to be clear whether it is necessary to prove general causation or specific causation. General causation refers to the ability of a chemical to cause an effect, not that there is any conclusion that such chemical caused an effect in a particular person under a specific set of conditions. If general causation has not been established in the literature then it is usually necessary to conduct a study to establish this finding. This is usually in the form of an epidemiological study, comparing two populations, one exposed and one not exposed or exposed to substantially less chemical. There are rare exceptions, usually involving rare conditions that might require somewhat less proof.
When is general causation a key? Usually either when attempting to establish a class of people exposed and presumably exibiting similar symptoms. In this case such discussion focuses on the commonality of the exposure and effects of the chemical on a population, without actually pinpointing cause in any particular person at that stage.
Specific causation requires that general causation has been established in the literature; the fact that a chemical can, under certain circumstances, cause an effect, is one piece of evidfence necessary to prove causation.
Following are five key steps:
1. Demonstrating through the literature that a chemical can cause such an effect. It is important to present this separate from the case at hand, that is, usuing one's client's condition as part of the proof is not a strong way to present causation. Multiple evidence should be relied on: epidemiological, animal studies, case studies in medicine, in vitro studies. Rather than simply explaining a 'laundry list' of data, the connection should be made, suggesting that each type of evidence supports the other. This makes a better narrative and ties all the data together into a whole stronger than the individual parts.
2. Explain what exposure is and how it differs from dose (see the Exposure page). Explain the different types of exposure (acute, chronic, continuous, periodic) and how this affects dose. Explain that although dose determines effect--the greater the dose the greater the effect--that it is usually not possible to measure exposure and determine dose precisely because it is usually done retrospectively
and for the dose, there are so many unknown factors that cannot be precisely determined. This however is not an impediment to determining exposure through use of a surrogate, such as proximity to a site of chemical release, length of exposure, markers of exposure (blood lead, for example). Explain that this is standard scientific procedure, regularly used in the peer reviewed scientific literature.
3. Determine health status of affected indivdiual. This should be broken down into a number of categories, with each presented as separate and emphasis placed as required, depending on the circumstances of the case. What was the condition at the time of exposure (that is, right as it was about to occur). Is there evidence to support this? What was the condition in the hours (or minutes) after exposure, up to a few days. This acute phase is often quite distinct from what occurs during the next week to a few weeks. A third phase is what happens over the next few months. Depending on the type of effect, there may be another, longer term phase of a year or longer, in which the condition continues at a plateau or worsens, or gradually improves. How do these time frames fit with what is known about general causation of the chemical? And last what was the person's medical history, both in childhood and as an adult, if that applies? Are there good medical records to support this and prescriptions? If not, how will that be addressed?
4. Are there alternative explanations for what occurred? Other exposures either at the time of the exposure in question, or at earlier times that could have increased susceptibility? Included in alternative explanations is whether there is simply not sufficient information or too much conflicting information to arrive at any explanation with any degree of certainty. It is important to be the 'devil's advocate' and show that this was thought through. A legitimate conclusion has to be more than the 'last one standing'.
5. Finally, it is important, for the first time, to bring together elements 1-4 and show how and why they fit and that that fit is the only reasonable explanation. These pieces should fit together like pieces of a jig saw puzzle, each complimenting the other and forming a picture that is undeniably specific causation.