2008 reported that 9799 of the total elec tromagnetic

(2008) reported that 97–99% of the total elec-
tromagnetic energy deposited in the brain is
absorbed at the side of the head the phone is
held during calls. Because of this asymmetry,
an e ff ect at the site of the growing tumor is
expected only or primarily for ipsilateral use.
ere is no objective method to retrospectively
assess side of the head the phone has been
used. Asking a person about this aspect of use
could result in bias. A person may be inclined
to suspect mobile phone use as a causal fac-
tor and may therefore tend to report using it
at the same side as the tumor has occurred.
On the other hand, the reverse also may be
claimed—that a person wants to dismiss the
possibility that using the phone has anything
to do with the disease and is therefore falsely

Mobile phones and cancer
Environmental Health Perspectives
t
VOLUME
117 |
NUMBER
3 | March 2009
321
reporting the opposite side of use. Even if
a patient does not intentionally distort the
answer, recent surgery may cause memory
deficiencies leading to recall bias. Hepworth
et al. (2006) argued that the reduced risk on
the contralateral side indicates such recall bias.
However, this risk reduction was due to an
artifact of the method applied. Estimate of
relative risk for contra lateral mobile phone
use was based on nonregular and ipsilateral
phone users as reference. It follows that when-
ever the relative risk of ipsilateral phone use is
> 1, the relative risk of contra lateral use must
be < 1 [the expected value of the OR in this
case is ( Q
o
+ Q
i
)/( Q
o
+ ZQ
i
), where Q
o
is the pro-
portion in the population of nonusers, Q
I
is
the proportion in the population of ipsilat-
eral users, and Z is the OR for ipsilateral use].
All meta-analytical ORs for ipsilateral mobile
phone use are > 1, and those for glioma and
acoustic neuroma are statistically significant. If
there was no misclassification bias in controls
and perfect sensitivity, then a small recall bias
in the direction of a preference for reporting
mobile phone use at the side of the tumor of
about 3% would reduce these enhanced ORs
for long-term ( ≥ 10 years) use to 1. However,
considering overall results for ipsilateral use,
recall bias must reduce specificity in cases by
30–40% to remove the observed enhanced
risk. e specificity that reduces an observed
increased OR to 1 is given by [1+( Z *–1) Q ]
–1
,
where Z * is the observed OR and Q is the
exposure prevalence in the population, given
that sensitivity in both cases and controls
and specificity in controls are 1 (Rothman
et al. 2008). For example, taking the study
of Hardell et al. (2005a) with an overall OR
for ipsilateral mobile and cordless phone use
of approximately 3.0 for acoustic neuroma
and a prevalence of about 23% of ipsilateral
mobile or cordless phone use, the specificity
must be as low as 68% to remove the observed
e ff ect. at is, 32% of those not exposed at
all or not on the side of the tumor must have
falsely stated they have been exposed. In other
words, more than half of mobile phone users
among cases and none among controls must
have given the wrong side of the head for