Selection bias in case-control studies of cell phones and brain tumours
Finland is one of the countries participating in the international case-control study of cell phone use and brain tumours (INTERPHONE). The authors of a recent article investigated whether there was any evidence of selection bias in their study. In other words, they attempted to determine whether there was a difference in cell phone use between those who agreed to participate in the case-control study and those who declined to participate. They also investigated whether any observed differences had an impact on the findings with regard to brain tumour risk. They found that non-participants were less likely to regularly use a cell phone, and that this tended to move the odds ratio further below unity, although the effect was not "substantial".
Reference: Lahkola A, Salminen T, Auvinen A. Selection bias due to differential participation in a case-control study of mobile phone use and brain tumors. Ann Epidemiol 2005;15:321-325.
There have been a number of studies of the possible effects of cell phones on brain function, with varying results. Schmid and colleagues recently investigated the effects of a 1.97 GHz UTMS-like signal on visual perception, using a battery of four tests. They found no statistically significant differences between the exposure conditions and sham exposure.
For more, see "Research - Clinical Experiments - Cognitive function".
Schmid G, Sauter C, Stepansky R, Lobentanz IS, et al. No influence on
selected parameters of human visual perception of 1970 MHz UMTS-like
exposure. Bioelectromagnetics 2005;243-250.
There has been ongoing controversy about whether the exposure level of radiofrequency (RF) energy from the use of a cell phone next to the head is higher for children than for adults. This topic has been discussed in "What's New" of September '03, March '04, and April '05. Bit-Babik and colleagues used a commercial Finite-Difference-Time-Domain (FDTD) numerical code to compute locally averaged SAR in two different anatomically correct adult and child head models using the IEEE standard averaging logarithm. Modeling and experimental measurements were also made using three spheres filled with a tissue-equivalent mixture, to approximate heads of increasing size. The peak 1- and 10-g average SAR values and electromagnetic energy penetration depths were not significantly different for child and adult heads exposed to the same RF-energy transmitting device. The authors suggest that the differences that were reported in other studies might be due to use of different algorithms for calculating spatial averaged SARs. They make a plea for standardization of "numerical models, definitions, positions, procedures an algorithms for SAR calculations".
Bit-Babik G, Guy AW, Chou CK, Faraone A, et al. Simulation of exposure
and SAR estimation for adult and child heads exposed to radiofrequency
energy from portable communication devices. Radiat Res 2005;163:580-590.
Various Swiss agencies sponsored an examination of the feasibility of future epidemiological studies on health effects or effects on well being from environmental sources, with particular emphasis on mobile telephone base stations. The final report of the committee has now been published. It gives a detailed analysis of dosimetric approaches, epidemiological issues, past and current research, and requirements for future studies.
Study on the feasibility of epidemiological studies on health effects
of mobile telephone base stations - final report. Neubauer G, Roosli
M, Feychting M, Hamnerius Y, Kheifets L, Kuster N, Ruiz I, Schuz J,
Uberbacher R, Wiart J. March, 2005.