Why are the findings from different studies of cell phone use and cancer risk inconsistent?
A limited number of studies have shown some evidence of statistical association of cell phone use and brain tumor risks, but most studies have found no association. Reasons for these discrepancies include the following:
- Recall bias, which may happen when a study collects data about prior habits and exposures using questionnaires administered after disease has been diagnosed in some of the study participants. It is possible that study participants who have brain tumors may remember their cell phone use differently than individuals without brain tumors. Many epidemiologic studies of cell phone use and brain cancer risk lack verifiable data about the total amount of cell phone use over time. In addition, people who develop a brain tumor may have a tendency to recall using their cell phone mostly on the same side of their head where the tumor was found, regardless of whether they actually used their phone on that side of their head a lot or only a little.
- Inaccurate reporting, which may happen when people say that something has happened more or less often than it actually did. People may not remember how much they used cell phones in a given time period.
- Morbidity and mortality among study participants who have brain cancer. Gliomas are particularly difficult to study, for example, because of their high death rate and the short survival of people who develop these tumors. Patients who survive initial treatment are often impaired, which may affect their responses to questions. Furthermore, for people who have died, next-of-kin are often less familiar with the cell phone use patterns of their deceased family member and may not accurately describe their patterns of use to an interviewer.
- Participation bias, which can happen when people who are diagnosed with brain tumors are more likely than healthy people (known as controls) to enroll in a research study. Also, controls who did not or rarely used cell phones were less likely to participate in the Interphone study than controls who used cell phones regularly. For example, the Interphone study reported participation rates of 78 percent for meningioma patients (range 56–92 percent for the individual studies), 64 percent for the glioma patients (range 36–92 percent), and 53 percent for control subjects (range 42–74 percent). One series of Swedish studies reported participation rates of 85 percent in people with brain cancer and 84 percent in control subjects
- Changing technology and methods of use. Older studies evaluated radiofrequency energy exposure from analog cell phones. However, most cell phones today use digital technology, which operates at a different frequency and a lower power level than analog phones. Digital cell phones have been in use for more than a decade in the United States, and cellular technology continues to change. Texting, for example, has become a popular way of using a cell phone to communicate that does not require bringing the phone close to the head. Furthermore, the use of hands-free technology, such as wired and wireless headsets, is increasing and may decrease radiofrequency energy exposure to the head and brain.