Abstract
Epidemiological studies are an important source of knowledge in the assessment of the effects
of ELF electric and magnetic field on health. We will focus on the assessment of exposure to
50160 Hz magnetic fields in epidemiological studies, in order to highlight the importance and
the difficulties of this assessment. The different methods of exposure assessment, their
advantages and disadvantages have been extracted from a review of the literature.
We based our review on the studies of childhood leukaemia. These exposure assessment
methods result in a single value when using wiring code, distance or calculation, in several
values when using measurement in space or time. It is therefore necessary to choose a single
indicator representing the exposure of the person but there is no demonstrated relationship
between any magnetic field indicator and illness. It is also necessary to define a threshold to
classify subjects as exposed or non-exposed: 0.3 or 0.4 μT, 50 m or 100 m, etc.
In conclusion, to assess the exposure, the underlying epidemiological hypothesis must be first
defined. Then the exposure assessment method must be chosen (calculation, measurement,
distance?), with the exposure indicator (mean, median, 90th percentile?). All this should be
precisely described in the methodology and validated before data collection and the statistical
part of the study.
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