General causation is about populations. This is about one person, their exposure, their history, and every other thing that could explain their diagnosis.
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Specific causation asks whether the exposure caused this claimant's disease. It is a clinical judgement rather than a statistical one, usually reached through differential etiology — assembling the plausible causes of this person's condition and reasoning about which can be ruled in or out on the individual facts. That process requires the exposure estimate to be adequate, the latency to be consistent with the disease, and the alternative explanations to be genuinely addressed rather than acknowledged and dismissed. Courts scrutinise the last point heavily: failure to account adequately for obvious alternative explanations is among the most frequently cited grounds for excluding a causation opinion, and it is the grounds most within the expert's control.
Each element is separately attackable, and each has been the basis of successful exclusion.
That this person's dose reached a level the general causation evidence actually speaks to — the link back to the exposure reconstruction.
Whether the interval between exposure and diagnosis fits what is known about the disease. Too short is as problematic as too long.
Identifying every plausible cause of this condition, including those unhelpful to the retaining party.
Explaining on the individual's facts why other candidates are excluded or are less probable — the step courts examine most closely.
Genetics, comorbidities, age at exposure, and other factors bearing on this person specifically.
An opinion tied to the actual clinical record rather than to the litigation narrative.
How the opinion is constructed and tested.
A matter can carry strong general causation and still fail entirely here.
Courts examine whether the expert adequately accounted for obvious alternatives. An opinion that lists other possible causes and dismisses them without individual reasoning is far weaker than one that engages each on this claimant's facts.
Not every conceivable one, but every reasonably plausible one, and the reasoning has to be individual rather than generic. Differential etiology does not require eliminating all alternatives with certainty — that standard would be impossible for diseases with idiopathic cases. It requires that plausible alternatives be identified and addressed on this person's facts, with an explanation of why the exposure remains the more probable explanation. Opinions excluded on this ground usually failed to engage rather than failed to persuade.
It is a genuine difficulty and it must be confronted rather than avoided. Where a large proportion of cases have no identified cause, the expert cannot exclude the possibility that this case is one of them, and an opinion claiming otherwise overstates. What can be done is to reason from the specifics — an unusually high exposure, an unusually early age at onset, a presentation atypical of the idiopathic form, or the absence of the usual risk factors. Courts have accepted such reasoning where it is grounded in the individual record, and rejected it where it amounted to assuming the answer.
The causation opinion inherits that uncertainty, which is why the two workstreams cannot be run independently. If the exposure reconstruction supports a wide range, the specific causation opinion has to be defensible at the low end of that range, or explain why the higher end is the more probable. Experts who take the upper bound of an exposure range as their working figure, without addressing why, hand the opposing side a straightforward line of attack that reaches both opinions at once.
Sometimes, and it carries the advantage of direct familiarity with the patient — but it also carries characteristic vulnerabilities. Treating physicians often have not reviewed the exposure evidence, may not have performed a differential aimed at causation as opposed to treatment, and can be shown to have accepted the exposure history as the patient reported it. Where a treating physician does offer the opinion, it is materially stronger when they have reviewed the exposure analysis and conducted a documented differential, rather than relying on clinical impression.
Describe the claimant's exposure and diagnosis. We will scope it and connect you with the right expert.