In order to assess and verify the effects of electromagnetic fields on the body or on general health, epidemiological studies as well as medical/biological studies have to be taken into account. Both types of studies have certain advantages and disadvantages which have to be considered during the evaluation process. The advantage of epidemiological and experimental medical/biological studies on humans is that they are carried out directly on humans, whereas their disadvantages are that in many cases the sample sizes are too small, often with insufficient retrospective data and lacking statistical power. Thus it is difficult to prove an actual association between a possible cause (e.g. a magnetic field) and an observed effect (e.g. a disease).
Moreover, the causality of an environmental factor, like electromagnetic fields, for a disease is hard to prove with the help of an epidemiological study. Additional in vitro and animal studies are necessary to confirm possible effects, reveal underlying mechanism of actions and to test hypotheses. Animal and in vitro studies provide more reliable results than epidemiological studies, because of standardized procedure protocols and larger sample sizes especially in cases where the effects are weak and hard to detect. However, the disadvantages are the difficulties in transferring the results to humans.
Evidence of an effect can be only shown by gathering and comparing the results of all types of studies. Only if the results of epidemiological, animal and in vitro studies give clear evidence of a certain effect, is it possible to call it a scientifically evidence-based association. Furthermore, it should be kept in mind that an effect does not necessarily have to mean an adverse health effect.