2008 reported that 9799 of the total elec tromagnetic

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(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
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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
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