In epidemiological studies, the distribution and determinants of health events of populations are studied, to try to determine the cause of the events.

There are two main types of epidemiological studies:

  • Case control: This type of study starts with the identification of a group of persons with the disease of interest, and uses for comparison a suitable control group of persons without the disease. The two groups are then compared with respect to possible causative factors.
  • Cohort: In this study a population (i.e. a cohort) is defined according to the presence or absence of a factor that might influence the probability of occurrence of a given disease. The cohort is then followed to determine if those exposed to the factor are indeed at greater risk of the disease.

Challenges: The design, execution and interpretation of epidemiological studies of the association between human health, or disease, and EMF exposures are difficult for a number of reasons (Phillips, 1998; Savitz, 1993; UNEP/WHO/IRPA, 1993, Swerdlow, 1999, Ahlbom, 2004).

  • The RF far-field radiation emitted from a mobile phone base station can be affected by many factors. These include the type of mobile phone service, the antenna characteristics, the height at which the antenna is sited, the number of proximal antenna sites, the number of users in the area, and structures or buildings that may impede the energy. An example of the variability that can exist in different locations was seen in the Health Canada (1997) study of RF field measurements of Vancouver-area schools that had either a PCS or an analog cellular base station antenna nearby. Health Canada found that maximum outdoor power density recorded varied from 230 to 6,200 times below the exposure limit specified by Safety Code 6, and that the maximum indoor measurements varied from 4,900 to 59,000 times below the limit. To obtain accurate far-field exposure data for an epidemiological study, multiple individual measurements of each antenna site in question should be made.

  • It is also very difficult to obtain accurate exposure assessments from near-field RF sources such as a hand-held unit. Power absorption from the antenna of a hand-held wireless telephone is very heterogeneous, and is dependent on a number of physical factors related to the power level of the RF signal. These include the distance of the user from the base station, the interference of the signal by buildings or other structures, and the direction the user is moving in relation to the antenna (ICNIRP, 1996, Ahlbom, 2004). The amount of RF absorption is also dependent on the duration of use, the number and length of individual calls, and any other 'individual habits of use' (Rothman, 1996). The latter include the angle at which the phone is held and the tendency to use one or other side of the head.

  • Another challenge in observational studies is the selection of appropriate control groups. Most individuals are exposed to varying amounts of background EMF depending on their history of use of electrical devices at home and work, and proximal location to telecommunications transmitters or electrical power distribution sources.

  • It is very difficult to establish EMF exposure in individuals over a meaningful period of time.

  • Reconstruction of an exposure history without having direct measurements requires a number of assumptions, which may or may not be valid.

  • Recall bias is common in case-control studies. This occurs when there is a systematic error due to differences in accuracy or completeness of recall of prior experiences. For example, brain tumour patients may be more likely than controls to misrepresent their use of a cell phone.

  • Selection bias may also be present (Lahkola, 2005). This occurs when there is a systematic difference in characteristics of those agreeing to participate in a study and those who do not.

  • A major problem is the control of confounding exposures (other factors that may influence an outcome and distort an apparent effect).

  • The temporal relationship between exposure and disease is often unclear.

  • The relatively recent advent of wireless technologies makes it more difficult to detect an adverse health outcome with a long latent period, such as most forms of cancer.

  • Many of the cancers studied are rare diseases and therefore it is challenging to:
    • obtain large sample sizes,
    • perform prospective cohort studies because of the need to observe a large number of individuals over time to obtain a statistically adequate number of cases,
    • examine specific subtypes of cancers (e.g., astrocytomas, gliomas) that might have different etiologies in relation to electromagnetic exposures.

A detailed examination of the issues surrounding epidemiological studies of health effects of base stations can be found in:
Feasibility of future epidemiological studies on possible health effects of mobile telephone base stations (Neubauer, 2007).

In this section we review studies on the association between RF radiation and health effects, mainly cancer.
All the studies suffer from the major weakness that exposure assessment is imprecise. The difficulties with exposure assessment in radiofrequency radiation studies are discussed in another section. The striking finding in the cancer studies is the lack of consistency with regard to cancer types or strength of association.

Reviews of epidemiological studies were conducted by Elwood (1999, 2003) and by Moulder et al. (1999). Breckenkamp (2003) reviewed cohort studies involving potentially high-exposed occupational groups. The references to these papers are given in the "Bibliography" section. Other reviews were undertaken by the Expert Panel of the Royal Society of Canada ( and by the Independent Expert Group on Mobile Phones ( A review of primary brain tumours (Wrensch, 2002) stated that "studies of cell phone use …. have found little to support a causal connection with brain tumours; caveats remain". Other reviews have been conducted by Jauchem (2003), Kundi (2004), Ahlbom (2004), and Moulder (2005) ), and Ahlbom (2005) .
Kan (2007) conducted a meta-analysis of cell phone use and brain tumour.

Elwood in his latest review (2003) offers this overall assessment:

"The epidemiological results fall short of the strength and consistency of evidence that is required to come to a conclusion that RF emissions are a cause of cancer. Although the epidemiological evidence in total suggests no increased risk of cancer, the results cannot be unequivocally interpreted in terms of cause and effect. The results are inconsistent, and most studies are limited by lack of detail on actual exposures, short follow-up periods, and the limited ability to deal with other relevant factors. In some studies, there may be substantial biases in the data used. For these same reasons, the studies are unable to confidently exclude any possibility of an increased risk of cancer. Further research to clarify the situation is justified."

Kundi et al. (2004) agree that all studies have some methodological deficiencies, but their overall conclusions are somewhat different: "...all studies approaching reasonable latency found an increased cancer risk associated with mobile phone use".

The studies reviewed in this section can be grouped under the headings "Studies examining cell phone use", and "other epidemiological studies". The latter is divided into "studies of general populations", "Studies of military personnel", and "studies of other occupations". All the research papers are listed in the reference section at the end of each subsection, in the alphabetical order of the first authors.

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