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David Michaels Speaks at ISEE Meeting on Data Re-analysis

September 4 - SKAPP Director David Michaels delivered a presentation, “Data Re-Analysis: A Tool for Manufacturing Uncertainty,” at the annual meeting of the International Society for Environmental Epidemiology in Paris, France. (Read the abstract) The paper was part of a session devoted to discussing the proposed “Guidelines for Ethical Reanalysis and Reinterpretation of Another’s Research.”

Presentation Summary
“Product defense” consultants, hired by industries whose products are the subject of regulation by government, generally try to manufacture uncertainty about the products’ harmful effects. Data re-analysis is one tool for manufacturing uncertainty, and Michaels offered the example of hexavalent chromium to demonstrate how product defense firms use it.

Hexavalent Chromium
In the 1990s, the US Occupational Safety and Health Administration (OSHA) proposed lowering its permissible exposure limit (PEL) for hexavalent chromium, Cr(VI), a known carcinogen used in chrome plating and in the production of metal alloys and pigments. Consultants for an industry group obtained the raw data from an Environmental Protection Agency study that had shown a clear dose-response relationship and a significantly elevated risk of lung cancer for workers with lifetime exposures at the level of 1 microgram per cubic meter. The consultants produced two re-analyses, both using new reference populations and one using a simulated cohort that found no excess lung cancer mortality risk in workers exposed above the current PEL of 52 micrograms.

OSHA rejected those two re-analyses, but requested additional data on cohorts with lower exposures. The industry commissioned a study of four newer chromium facilities, and it found a significantly elevated risk of lung cancer mortality associated with low exposures to Cr(VI). Rather than provide that data to OSHA, the consultants conducting the study broke the results into two smaller studies that showed no increased cancer risk for workers exposed to low levels of Cr(VI), and submitted those results to the agency just before its comment period ended.

OSHA eventually issued a new PEL of 5 micrograms – lower than its old limit but higher than the one it initially proposed.

Benzene
A study by Robert Rinsky and colleagues, published in the New England Journal of Medicine in 1987, found a clear dose-response relationship between occupational benzene exposure and leukemia and concluded that “an exponential decrease in the risk of death from leukemia could be achieved by lowering occupational exposure.” Three re-analyses published in the following years criticized his risk estimates and argued that the workers in that study experienced exposures much higher than previously estimated, resulting in lower leukemia risk.

A study conducted by scientists at the US National Cancer Institute and the Chinese Academy of Preventive Medicine, by Richard Hayes and colleagues, published in the Journal of the National Cancer Institute in 1997, studied hematologic neoplasms more than 100,000 workers (nearly 75,000 of whom were exposed to benzene) from 672 Chinese factories and found a dose-response curve consistent with that of Rinsky et al. Documents obtained from the petroleum industry show that the industry is undertaking a similar research study – focusing on the hematological effects of benzene exposure in workers in Shanghai – in order to refute these findings.

Ethical Re-analysis
Both of these studies – Hayes’s study and the industry study apparently being conducted – may become subjects of re-analyses. Michaels stressed that there are many positive reasons for conducting re-analysis, and distinguishes ethical re-analysis from that performed with the goal of showing a product to be less harmful. Members of the ISEE have begun to address this issue in “Toward Guidelines for the Ethical Reanalysis and Reinterpretation of Another’s Research,” published in Epidemiology in May 2006.