rate ratio

A rate ratio is a number that compares how often a disease occurs in one group versus another over a given time period. For example, if asbestos-exposed workers develop mesothelioma at 10 times the rate of unexposed people, the rate ratio is 10. It is one of the core measurements epidemiologists use to show that an exposure raises the risk of a disease.

Origin

The rate ratio emerged from 20th-century epidemiology as researchers developed formal ways to compare disease frequency between populations. It became central to occupational health studies in the 1950s-1970s, including the foundational asbestos cohort studies by Richard Doll (1955) and Irving Selikoff (1964) that quantified the elevated cancer rates among asbestos workers.

Significance in Asbestos Context

Rate ratios are often the headline numbers experts cite to show that asbestos causes disease. In asbestos litigation, plaintiffs' experts may point to rate ratios from studies of insulators, shipyard workers, or miners (sometimes 5x, 10x, or even higher for lung cancer and mesothelioma) to demonstrate that the exposure is a meaningful cause of disease in people like the patient. Defendants frequently argue that a particular study's rate ratio does not apply to the specific product, fiber type, or exposure level in the case. Understanding which studies and which rate ratios your experts rely on can help you follow the technical back-and-forth in depositions, expert reports, and trial.

Example Sentence

The plaintiff's epidemiologist testified that workers with comparable chrysotile exposure showed a mesothelioma rate ratio of approximately 8 compared to the general population.

Related Terms

Relative Risk, Standardized Mortality Ratio (SMR), Cohort Study, Attributable Risk, Dose-Response, Epidemiology

Notes

• Ask your legal team which specific epidemiological studies and rate ratios their experts are relying on, and whether those studies match your occupation and fiber exposure.
• Watch for the distinction between rate ratio, relative risk, and odds ratio. Defense experts sometimes challenge plaintiffs' experts on using the wrong measure for the study design.
• Rate ratios apply to groups, not individuals; your experts will need to connect population-level findings to your specific exposure history through additional analysis.
• Preserve any employment, union, or military records that place you in an occupational cohort similar to those studied in published rate-ratio research, as this strengthens the link.