Regarding the World Health Organization's (WHO) recent finding [PDF] that mobile phones might possibly maybe could-be perchance correlated with a slightly higher rate of brain cancer, one should keep in mind, epidemiologist John Ioannidis' admonitions about the public choice pressures on epidemiologists. In Scientific American, Ioannidis warns against "An Epidemic of False Positives":
False positives and exaggerated results in peer-reviewed scientific studies have reached epidemic proportions in recent years. The problem is rampant in economics, the social sciences and even the natural sciences, but it is particularly egregious in biomedicine. Many studies that claim some drug or treatment is beneficial have turned out not to be true. We need only look to conflicting findings about beta-carotene, vitamin E, hormone treatments, Vioxx and Avandia. Even when effects are genuine, their true magnitude is often smaller than originally claimed.
The problem begins with the public's rising expectations of science. Being human, scientists are tempted to show that they know more than they do. The number of investigators—and the number of experiments, observations and analyses they produce—has also increased exponentially in many fields, but adequate safeguards against bias are lacking. Research is fragmented, competition is fierce and emphasis is often given to single studies instead of the big picture.
And when the postulated effect is tiny, what can epidemiology really tell us? As I have reported [PDF] elsewhere:
It is not easy to sort actual risk factors from the statistical background noise of confounders and biases. "With epidemiology you can tell a little thing from a big thing. What's very hard to do is to tell a little thing from nothing at all," said Michael Thun, an American Cancer Society epidemiologist in 1995. Former Boston University epidemiologist Samuel Shapiro agrees: "In adequately designed studies we can be reasonably confident about big relative risks, sometimes; we can be only guardedly confident about relative risks estimates of the order of 2.0, occasionally; we can hardly ever be confident about estimates of less than 2.0, and when estimates are much below 2.0, we are simply out of business. Epidemiologists have only primitive tools, which for small relative risks are too crude to enable us to distinguish between bias, confounding and causation." …
"Some may argue that it is of public health importance to identify and evaluate possible causal implications of small relative risks because for common diseases these can translate into large absolute risks," writes Shapiro. But as he cautions his colleagues, "Unfortunately, however, not all questions are answerable even if we desperately want answers, and public health importance does not equate with scientific validity."
Let's take a brief look at the results of one of the bigger studies considered by the WHO panel in coming to its decision, the 13-nation case-control Interphone study [PDF]. The National Cancer Institute summarizes the results:
"A reduced odds ratio (OR) related to ever having been a regular mobile phone user was seen for glioma [OR 0.81; 95% confidence interval (CI) 0.70-0.94] and meningioma (OR 0.79; 95% CI 0.68-0.91), possibly reflecting participation bias or other methodological limitations. No elevated OR was observed ? 10 years after first phone use (glioma: OR 0.98; 95% CI 0.76-1.26; meningioma: OR 0.83; 95% CI 0.61-1.14). ORs were < 1.0 for all deciles of lifetime number of phone calls and nine deciles of cumulative call time. In the tenth [highest] decile of recalled cumulative call time, ?1640 h, the OR was 1.40 (95% CI 1.03-1.89) for glioma, and 1.15 (95% CI 0.81-1.62) for meningioma; but there are implausible values of reported use in this group. ORs for glioma tended to be greater in the temporal lobe than in other lobes of the brain, but the CIs around the lobe-specific estimates were wide. ORs for glioma tended to be greater in subjects who reported usual phone use on the same side of the head as their tumour than on the opposite side."
It's mildy amusing to note that mobile phone use appears to be prevent brain cancer among people who have ever made a cell phone call. Even among top ten percent of heavy users, their risk of brain cancer was well below Shapiro's 2.0 relative risk threshold.
Interestingly, as the number of cell phone subscriptions in the U.S. has risen from 1 million in 1987 to over 300 million today, the National Cancer Institute reports that brain cancer incidence [PDF] has been trending slightly downward.
Based on what is known so far, AT&T doesn't have to worry about me giving up my iPhone just yet.