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Epidemiology
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Epidemiology (from Greek epi “on, about“, demos “people“, logos “science, study“) is a scientific discipline dealing with the distribution of diseases within a population and with the factors influencing this distribution.
Radiation epidemiology particularly considers possible associations between ionising radiation (for instance from medical X-ray examinations, radiotherapy, or cosmic irradiation during long-distance flights) or non-ionising radiation (for instance radiation from mobile phones, cell towers, or electric and magnetic fields around high-voltage power lines) on the one hand, and the risk to develop cancer, eye cataract, or cardiovascular disease on the other hand.
Which methods are applied in epidemiology?
Experimental studies involve experiments conducted under controlled laboratory conditions, however this is not possible in humans for practical and ethical reasons. This is why so-called epidemiological studies are carried out.
Epidemiological studies are mere observational studies. These studies allow both the direct estimation of risk to man and risk level quantification. The most important kinds of epidemiological studies are so-called case-control studies and cohort studies. Basically there are the following four main types of epidemiological studies:
Cross-sectional studies
A cross-sectional study establishes and evaluates the correlation between exposure (e.g. measured exposure to electromagnetic fields of mobile phone base stations) and the outcome under consideration (e.g. sleep disorders or headache) at a given point in time.
These studies are only useful in cases of relatively frequent and acute diseases.
Ecological studies
“Ecological” studies use regionally or temporally aggregated data from sub-groups to determine the relationship between radiation and disease. Ecological studies are prone to errors because other risk factors are assumed to be uniformly distributed over the subgroups and no individual data are available.
This is exemplified by a Germany-wide comparison of lung cancer mortality rate and radon concentration in dwellings: the most important risk factor for lung cancer is smoking. If the regionally varying percentages of smokers are not accounted for in such a study, this may give rise to biased results with regard to the radon-induced lung cancer risk.
Cohort studies
In cohort studies a defined population comprising of individuals with or without exposure to a risk factor is followed-up over a defined period of time. For instance, the typical question posed in a cohort study is whether specific diseases occur more often in individuals with a history of high exposure than in individuals with a history of low or no exposure.
An example of a cohort study is the survey on 60 000 former uranium ore miners employed at the Wismut company conducted on behalf of the Federal Office for Radiation Protection (Bundesamt für Strahlenschutz, BfS). This study on uranium ore miners addresses cancer risk as a function of previous radiation exposure.
Case-control studies
The question under scrutiny in a case-control study is whether diseased individuals have been more often or higher exposed than comparable individuals without the disease in question. To that end, individuals exhibiting the disease have to be identified in the population under study. Since the study is confined to the diseased individuals (“cases”) and a comparable number of unaffected individuals (“controls”), the number of individuals involved in case-control studies can be considerably smaller than in cohort studies.
Case-control studies may also be nested in cohort studies whence additional data have to be collected for that particular subgroup of a cohort.
An example is the KiKK-study commissioned by the Federal Office for Radiation Protection, (Bundesamt für Strahlenschutz, BfS). In this study children which had been living in the vicinity of nuclear power plants in Germany and which developed leukaemia or other cancers were compared to children of the same age and sex living in the same region who did not develop any of these diseases. The question under study was whether diseased children (cases) lived closer to a nuclear power plant than children (controls) matched to them.
Epidemiological studies on behalf of the Federal Office for Radiation
Protection:
For instance, in the field of ionising radiation, the Federal Office for Radiation Protection (BfS) is conducting the largest cohort study on health effects of ionizing radiation
in former uranium ore miners employed at the WISMUT SDAG of the former GDR and has ordered the Study on Childhood Cancer in the Vicinity
of Nuclear Power Plants (KiKK-Study)
In the field of non-ionising radiation, the Federal Office for Radiation
Protection (BfS) has initiated and supported a great number of epidemiological
studies on potential health effects of radiofrequency radiation within the
scope of the German Mobile Telecommunications
Research Programme.
For further topical research projects see BfS Research Programme (2009–2013).
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