Kowall B, Breckenkamp J, Heyer K, Berg-Beckhoff G. German wide cross sectional survey on health impacts of electromagnetic fields in the view of general practitioners. Int J Public Health. Dec 18, 2009 Ahead of print.

A considerable proportion of western population expresses concern about electromagnetic fields (EMFs) and/or attributes health symptoms to EMFs. Many people who attribute their health problems to EMFs presumably go to see a general practitioner (GP). Therefore, GPs may play a major role in strengthening or weakening patients’ associations of symptoms with EMF.

The objectives of this study were to assess the proportion of GPs who associate health symptoms with EMF, to examine the role of selection bias in such surveys, and to examine factors associated with GPs’ perception of EMF risks.

Seven percent random samples were drawn from lists published by the 17 Regional Associations of Statutory Health Insurance Physicians. In total, 2,795 addresses were drawn and were arbitrarily distributed into 2 groups: 1867 GPs received a long self-administered postal questionnaire (4 pages), and 928 GPs received a short questionnaire (1 page). The long questionnaire was sent to non-responders once again 4 weeks later, and the short questionnaire twice (4 weeks and 8 weeks later).

The response rate was 49.1% for the short questionnaire and 23.3% for the long questionnaire. Participants in these 2 groups did not differ in terms of their demographic characteristics, the proportion of medical specialists, or in terms of proportion of physicians with additional education in alternative medicine. A proportion of 37.3% of the respondents to the short questionnaire and 57.5% of respondents to the long questionnaire responded positively to the question “Are there persons whose health complaints are caused by EMF when legal limit values are met?”. An analysis of late responders to the short questionnaire has shown that the proportion of positive response to this question was lower in late respondents (31.7%) than in intermediate (37.2%) and early respondents (41.8%). A proportion of agreement with this item estimated for the whole sample in a regression analysis was 29.3%. In the logistic regression analysis, 3 factors were significantly associated with the perception of EMF risks: GPs with additional education in alternative medicine were more often convinced of existence of EMF risks, GPs having confidence in the World Health Organization – less often; GPs in the Western and Southern parts of Germany more often believed in health impacts of EMF.

Interpretation and Conclusion
A considerable proportion of GPs in Germany (about 30%) attribute health complaints to EMFs, the notion that is supported by little scientific evidence. The proportion obtained from the short questionnaire is more valid than that obtained from the long questionnaire because the latter was distorted by selection bias: long questionnaires are more likely to be filled out by people with special interest in the topic of the survey. To avoid a strong selection bias in such surveys, it is recommended to use short questionnaires and to conduct late responder analysis.

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