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Lloyd Morgan's Column
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Commentary - Cellular Phones, Cordless Phones, and the Risks of Glioma and
Meningioma (Interphone Study Group, Germany)
Schüz et al., American Journal of Epidemiology Advance Access published
January 27, 2006
This study, similar to all Interphone studies published to date, has several
serious problems. For one, its core findings report no risk for glioma or for
meningioma from "regular" cellphone use ("regular" use is defined as at least
one incoming or outgoing call per week for 6 months or more). Yet, it reports a
2.2-fold risk of glioma after more than 10 years of cellphone use with a 94%
confidence that this risk is not due to chance. Also, it found a 1.96-fold risk
of high-grade glioma for women from "regular" cellphone use with a 98%
confidence. Given the specific problems of the study - all of which would
underestimate the risk of a brain tumor - these findings are ominous.
Here is a list of the main problems in this study:
- The definition of unexposed cases and controls included
subjects exposed to cordless phones. Previous studies have shown that cordless
phone use increases the risk of glioma [1] and
meningioma. [2] Including exposed subjects in the
unexposed group will cause an underestimation of risk.
- The definition of a "regular" cellphone user is so minimal that almost all
"regular" cellphone users would not be expected to be at risk, even if cellphone
use is found to create a very high risk of glioma and meningioma.
As mentioned earlier, regular use as defined by all Interphone studies, is "at
least one incoming or outgoing call per week for 6 months or more." As to
longer periods of "regular" cellphone use, this study reported only 14% of the
glioma cases and 6% of meningioma cases used a cellphone for 5 years or more;
for 10 years or more, the percentages are 3% and 1%, respectively.
To understand that "regular" cellphone use as defined in this study is so
minimal that risk ought not to be expected, even if there is a high risk
of glioma and meningioma from cellphone use, consider a hypothetical study of
smokers and the risk of lung cancer. Would a risk of lung cancer (which is a
high risk for smokers) be expected to be found for smokers who had smoked once a
week, for 6 months or more with only 12 subjects (3%) smoking for 10 years or
more?
- There is a strong possibility of selection bias. Some 30.5% of controls
refused to participate in the study compared to only 4.8% of glioma cases and
4.9% of meningioma cases. If a higher proportion of controls who participated -
compared to controls who refused participation - used a cellphone, then any risk
would be underestimated. This result - an underestimated risk - seems to be at
play in this study.
Some 58% of controls who refused to participate answered a question whether or
not they used a cellphone. These groups of non-participating controls - one of
both sexes between the ages of 40 and 59 years of age, and another of men
between 30 and 39 years of age - provided confirmation that a selection bias
problem indeed existed in this study. That is, these non-participating control
groups used cellphones less frequently than did the participating control
group.
[There were two small exceptions to this selection bias: Controls between 60
and 69 years who refused to participate, and those that did participate,
reported a common amount of cellphone use and so did not contribute, one way or
the other, to selection bias. This group represents roughly 15% of the total
controls. The only non-participating controls that reported higher use of
cellphones compared to participating controls were females 30-39 years of age.
This would have caused an overestimation of risk among a very small proportion
(about 8%) of all the controls.]
- Substantial funding of this, and all Interphone studies, comes from the
cellphone industry with a resultant, but undeclared, conflict-of-interest.
Though the study reports that this funding "was governed by agreements that
guaranteed complete scientific independence" it seems doubtful that this
"guaranteed" "scientific independence" is possible. Researchers' careers are
dependent on receiving research grants. Even with isolation of funding for a
specific study from the researchers themselves, the conflict-of-interest in such
funding is not resolved. Because the researchers know where the funding has come
from, the old adage, "Don't bite the hand that feeds you," becomes the effective
psychological reality (whether conscious or unconscious).
Friedman and Richter explored this concern by reviewing the conflict-of-interest
problems found in studies published in the New England Journal of Medicine and
The Journal of the American Medical Association during 2001. The paper found a
strong association between those studies whose authors had an economic conflict
of interest and, as well, reported positive findings (P <0.001, equivalent of
greater than a 99.9% confidence).[3]
In the case of cellphone studies, could the findings of these industry-funded
studies have a correlation with findings of no harm from cellphone use? It is
interesting to note that the Interphone studies, all receiving substantial
cellphone industry funding, consistently put forth press releases highlighting
the "no risk" findings from cellphone use. But the Hardell et al. studies - all
independently funded - consistently are finding a greater and greater risk from
cellphone use with each new study they publish.
References
[1] Hardell et al., 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 Feb;100(2):232-41.
[2] Hardell et al., Pooled analysis of two case-control studies on the use of
cellular and cordless telephones and the risk of benign brain tumors diagnosed
during 1997-2003; International Journal of Oncology 28: 508-518, 2006.
[3] Friedman and Richter, Relationship between conflicts of interest and
research results; J Gen Intern Med. 2004 Jan;19(1):51-6.
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