American Journal of Epidemiology Advance Access originally published online on June 27, 2006
American Journal of Epidemiology 2006 164(3):295-296; doi:10.1093/aje/kwj230
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Letter to the Editor |
THE AUTHORS REPLY
1 Institute of Medical Biostatistics, Epidemiology and Informatics, Johannes Gutenberg-University of Mainz, D-55101 Mainz, Germany
2 Institute of Cancer Epidemiology, Danish Cancer Society, DK-2100 Copenhagen, Denmark
3 Department of Epidemiology and International Public Health, Faculty of Public Health, University of Bielefeld, D-33501 Bielefeld, Germany
4 Unit of Environmental Epidemiology, German Cancer Research Center, D-69120 Heidelberg, Germany
(e-mail: joachim{at}cancer.dk)
We thank Mr. Morgan for his observations (1
). Mr. Morgan makes three comments on our recently published study (2). His first comment pertains to the definition of "regular" cellular telephone use. The point of specifying a "regular" cell-phone user was to define a referent group, since there were only a few "never" users in our study population. This definition of a referent group assumes no increase in brain tumor risk at exposure levels deriving from nonregular use of cell phones. This group was contrasted with various groups of persons with higher exposure, defined by time since first regular use, cumulative use, and a mixture of both (see table 3 in our paper (2)). Even long-term users in our study had barely more than 10 years of regular use and, in the beginning, were not heavy users; hence, we could not draw conclusions on heavy long-term use, as we expressed in our paper (2).
Second, Morgan speculates about possible effects of selection bias; however, self-critically, we provided much more information on this topic in figure 2 and the Discussion section of our paper (2). Morgan compares one of our risk estimates with one from another study by Hardell et al. (3); however, we cannot more deeply examine possible methodological influences that might explain the discrepant results, because essential information on materials and methods was not published for the other study. Furthermore, Morgan fails to mention that all of the other published papers on this topic (summarized in our Discussion (2)) show results that are more in line with our findings than with those of Hardell et al. (3).
Third, Morgan suggests that we have an ethical conflict because our study was partially funded by commercial interests. It has never been a secret that the Interphone Study receives supplemental funding from the mobile phone industry. The manner in which this has been done in order to guarantee scientific independence is clearly stated in our acknowledgments (the proportion of public funding for the German component of Interphone was 75 percent). We strongly believe that industry has a responsibility to support research into possible adverse health effects associated with the use of its products, and we do not see why such research should only be funded through public sources. The Interphone Study is an excellent example of how a firewall between industry and investigators can be implemented to guarantee the scientific independence of research.
ACKNOWLEDGMENTS
Conflict of interest: none declared.
References
- Morgan LL. Re: "Cellular phones, cordless phones, and the risks of glioma and meningioma (Interphone Study Group, Germany)." (Letter). Am J Epidemiol 2006;164:294–5.
[Free Full Text] - Schüz J, Böhler E, Berg G, et al. Cellular phones, cordless phones, and the risks of glioma and meningioma (Interphone Study Group, Germany). Am J Epidemiol 2006;163:512–20.
[Abstract/Free Full Text] - Hardell L, Carlberg M, Mild KH. Case-control study of the association between the use of cellular and cordless telephones and malignant brain tumors diagnosed during 2000–2003. Environ Res 2006;100:232–41.
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