Wednesday, September 19, 2018

EMF Research and the Weight of Scientific Evidence

We have all seen media articles that claim that a new study has “proven” a chemical or physical agent causes some health effect, usually cancer. While such results might look scary or at least surprising to the reader, scientists usually react differently and point to the “weight of scientific evidence”. What does this term mean and how does it apply to scientific studies related to electromagnetic fields (EMF) research?

As summarized in the MWF’s booklet on “20 years of research”,

The ‘weight of scientific evidence’ approach means that no single study can answer any scientific question, and must not be viewed in isolation but against the backdrop of previous research. Factors such as the quality of the data, consistency of results, nature and severity of effects and relevance of the information are all important considerations for experts to determine appropriate weighting to be given to the evidence. This approach is important to consider in research on radiofrequency (RF) electromagnetic field (EMF) health effects when individual studies provide different or conflicting results. Individual studies need to be seen in the light of the total research effort into mobile phone health and safety. Scientific investigation is subject to potential errors, personal opinions and uncertainties. This applies as much to research on RF EMF health effects as it does to all other areas of science.

The concept of “weight of scientific evidence” is not exclusive to research on EMF but is a key principle in scientific work. The European Food Safety Authority’s (EFSA) scientific committee has published for example a “Guidance on the use of the weight of evidence approach in scientific assessments”. In this Guidance it states:

Weight of evidence assessment is a process in which evidence is integrated to determine the relative support for possible answers to a scientific question. The term ‘weight of evidence’ on its own is the extent to which evidence supports possible answers to a scientific question. This is what is assessed by weight of evidence assessment, and can be expressed qualitatively or quantitatively. 

The European Commission’s Scientific Committee on Health, Environmental and Emerging Risks (SCHEER)  published in June 2018 a revision of their “Memorandum on weight of evidence and uncertainties”, which defines the weight of evidence as

A process of weighted integration of lines of evidence to determine the relative support for hypotheses or answers to a question. 

All of this does not mean that single studies are ignored or not important. They are integrated into the body of knowledge and put into context with all the other studies and research that have been carried out on the subject in question. As the World Health Organization  has stated, “(i)n the area of biological effects and medical applications of non-ionizing radiation approximately 25,000 articles have been published over the past 30 years.” And as a result “scientific knowledge in this area is now more extensive than for most chemicals.”


MWF’s “20 years of research” booklet (2018):

EFSA’s “Guidance on the use of the weight of evidence approach in scientific assessments” (2017):

SCHEER’s “Memorandum on weight of evidence and uncertainties” (2018):

World Health Organization: What are electromagnetic fields?