Meta-Analysis

A meta-analysis combines the results of many separate studies on the same question into a single overall estimate, using statistical methods that give more weight to larger or more precise studies. In asbestos science, meta-analyses have been used to estimate how strongly different fiber types cause mesothelioma and lung cancer.

Origin

The term "meta-analysis" was introduced by the statistician Gene Glass in 1976, though methods for combining studies are older. The technique spread through medicine in the 1980s and 1990s, and several influential asbestos meta-analyses were published around 2000 and after, including the Hodgson and Darnton analysis and the Berman and Crump analysis.

Significance in Asbestos Context

Meta-analyses are among the most-cited sources in asbestos litigation, because they appear to give a single number for questions like how much more potent amphiboles are than chrysotile in causing mesothelioma. Defense experts often rely on meta-analyses that rank chrysotile as much less potent; plaintiffs' experts point out that the results depend on which studies are included, how exposures in the original studies were estimated, and how differences between studies are handled. Combining studies that measured exposure very differently can produce a precise-looking figure that hides large uncertainty. A meta-analysis is also only as good as its underlying studies; it cannot remove biases that all of them share. Major public-health agencies, including IARC, have concluded that all commercial forms of asbestos, including chrysotile, cause mesothelioma and lung cancer. For patients and families, a meta-analysis in an expert report is evidence to be tested, not a final answer.

Example Sentence

The defense expert relied on a meta-analysis estimating that amphiboles were far more potent than chrysotile for causing mesothelioma.

Related Terms

Systematic Review, Berman-Crump Meta-Analysis, Epidemiology, Relative Risk, confidence interval, amphibole hypothesis, Chrysotile Defense

Notes

• Ask your lawyer which studies a meta-analysis included and left out; that choice often drives the result.
• A meta-analysis about fiber potency does not answer whether your own exposure caused your disease.