It is not possible for science to prove there is no risk. It is only possible for science to prove, under certain exposure conditions, that an effect does exist. Further, assessing a potential health hazard requires a comprehensive body of scientific evidence that is not likely to occur, in the case of RF, in the short term. A critical review of the science requires the consideration of relevant published studies where the evidence is evaluated on the merits of the research design and conduct of the study. Replication studies, which attempt to provide evidence for the same effect under the same conditions, are very important. Ultimately, an accumulation of well-designed and well-executed studies producing results of similar magnitude and strength provides increasing confidence of the absence or presence of a significant health effect. There are different types of research studies. The two main groups are experimental and epidemiological.
Epidemiological studies investigate associations between health effects, characteristics of people, and exposure to different factors. The advantages and disadvantages of these studies are discussed further in "Human Epidemiology". In experimental studies, sometimes called laboratory studies, the conditions of the study are under the control of the investigator.
More weight is placed on research involving human subjects. Some short-term human experimental studies have been done using RF radiation, but longer-term research, such as that needed to investigate a possible association with cancer, relies on epidemiological studies. Most laboratory studies are done on individual human or animal cells (in vitro) or on animals (in vivo). These are discussed at greater length in the introduction to "Clinical Experiments".
In general, there is an accepted hierarchy of research studies: Human research is considered more relevant than animal studies, which in turn are given greater credence than cellular studies. Even within animal research, some studies might contribute more than others to our understanding of association between human disease and, say use of cellular phones. Lifetime studies involving chronic exposure to RF radiation at cell phone frequencies and power might tell us more than short-term exposure to higher power radiation.A number of scientific groups and panels have issued detailed reports and these can be seen in "Review Panel Reports". These provide an overview of the health effects of exposure to radiofrequencies.
Useful sources of information about current research are the WHO and IEEE databases, which can be found at http://www.who.int/docstore/peh-emf/EMFStandards/who-0102/Worldmap5.htm
Summary of human research
In the sections to follow, the research studies examine the effects of exposure to either radiofrequency radiation (RFR) in general, or specifically to the radiation from cell phones.
The epidemiological studies mainly examine cancer, but a few concentrate on general health symptoms. The cancer studies are covered in detail in the "Epidemiology" section.
There are some studies relating to general health symptoms, covering
a variety of health issues.
In this section there are a variety of studies that examined other
biological health effects. They are summarized in detail in each