Doubling of Risk

Doubling of risk is the idea that if an exposure at least doubles a person's chance of getting a disease (a relative risk above 2.0), then it is more likely than not that the exposure caused that person's disease. Some courts use it as a way to prove specific causation from epidemiological studies.

Origin

The reasoning comes from the civil burden of proof: if exposed people get a disease more than twice as often as unexposed people, more than half of the cases among the exposed can be attributed to the exposure. The Texas Supreme Court relied on it in Merrell Dow Pharmaceuticals v. Havner (1997), a drug case, and courts in Texas and elsewhere have since applied the idea to toxic exposure claims.

Significance in Asbestos Context

The doubling idea comes up most often in asbestos lung cancer cases, because lung cancer also has other causes, especially smoking. The Helsinki Criteria, for example, treat about 25 fiber-years of cumulative exposure, or the presence of asbestosis, as enough to roughly double lung cancer risk. Defendants sometimes argue that a plaintiff must show that one company's product, by itself, doubled the risk, a burden that can be very hard to meet when a worker was exposed to many products. Plaintiffs answer that the rule misreads the science and that mesothelioma, which is rarely caused by anything but asbestos, should not be analyzed this way. How a state treats doubling of risk, and whether it applies to each defendant or to total exposure, varies widely, so the rule can shape what kind of exposure and expert evidence a case needs.

Example Sentence

The defense expert argued that the plaintiff's exposure to the pump maker's gaskets was too small to show a doubling of risk for lung cancer.

Related Terms

Relative Risk, Specific Causation, General Causation, Helsinki Criteria, Fiber Year, Preponderance of the Evidence, Lung Cancer, Substantial Factor Test

Notes

• Ask your lawyer how your state treats doubling-of-risk arguments; the rules differ a great deal.
• A detailed work history, with years, jobs and products, helps experts estimate cumulative exposure.
• Smoking history matters in lung cancer cases; give your lawyer an accurate account.