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Randomized controlled trials are under-used in environmental health research

Randomized controlled trials, the scientific method which underlies so much of modern medicine, make up a tiny proportion of environmental health research studies. Ryan Allen, of Simon Fraser University in Canada, writing with colleagues in PLOS Medicine, describes how such trials have historically been under-used, and discusses how much they have to offer in identifying environmental risks and improving human health.

Observational studies are often unable to conclusively distinguish between two factors that are associated by co-incidence and two that are linked by a causal relationship. Randomized controlled trials can more definitively distinguish the difference between the two. Despite this, note Allen and colleagues, when it comes to environmental health, such key trials “comprise less than 1% of research publications in the field.”

There are often good reasons for not using a randomized trial in environmental health research. The link between smoking and cancer, for example, was reliably established based purely on observational evidence. Many problems, though, could be better understood through the use of randomized trials. Allen and colleagues describe some of these problems, and outline the potential for trials to produce knowledge that could save lives and make better use of valuable resources. They note examples of good practice, with randomized trials being used to explore the most effective ways of combating poverty, promoting international development and exploring questions about environmental pollution.

“Randomized controlled trials are standard practice in clinical and pharmaceutical research,” conclude the authors, “but have not been embraced by environmental health researchers.” Without overlooking the value of observational science when it comes to environmental health, and with a proper appreciation of the practical and ethical considerations involved in conducting randomized controlled trials, this paper nevertheless draws attention to an under-used tool for exploring our world and for finding ways to make it healthier.


Randomized Controlled Trials in Environmental Health Research: Unethical or Underutilized? Allen RW, Barn PK, Lanphear BP, PLoS Med, doi:10.1371/journal.pmed.1001775, published 6 January 2015.

No funding was received for this work.

Competing Interests: RWA has received grant and/or contract support from the Canadian Institutes of Health Research, Health Canada, the British Columbia (BC) Ministry of Environment, the BC Lung Association, and the Allergy, Genes, and Environment Network. He has received honoraria for committee participation, peer review, etc. from the BC Lung Association, the Health Effects Institute, and the US EPA. He has received travel funds from the Universidad del Valle (Colombia), the Montreal Department of Public Health, and the Allergy, Genes, and Environment Network. PKB has received research funding, scholarships, and awards from the Air & Waste Management Association, British Columbia Environmental and Occupational Health Research Network, Canadian Institutes of Health Research, Canadian International Development Agency, Fraser Basin Council, Provincial Health Services Authority, Simon Fraser University, and the Vancouver Foundation. BPL has served as an expert witness and as a consultant to the California Attorney General’s Office and in a California public nuisance case against the paint and pigment industry, but he has not personally received any compensation for these services. BL has also served as a paid consultant on a US Environmental Protection Agency research study and the California Department of Toxic Substances. He has received NIH, US EPA and Canadian Institutes for Health Research grant support.