In response to the post The bane of many causes in the context of mobile phone use and brain cancer, Robert Erikson wrote:

The true control here is the side of the head of the tumor: same side as phone use or opposite side. If that is the test, the data from the study are scary. Clearly tumors are more likely on the “same” side, at whatever astronomical p value you want to use. That cannot be explained away by misremembering, since an auxiliary study showed misremembering was not biased toward cell phone-tumor consistency.

A strong signal in the data pointed by Prof. Erikson is that the tumors are overwhelmingly likelier to appear on the same side of the head as where the phone is held. I’ve converted the ratios into percentages, based on an assumption that the risk for tumors would be apriori equal for both sides of the head.

There is a group of people with low-to-moderate exposure and high lateral bias, but the bias does increase quite smoothly with increasing exposure. It’s never below 50%.

But even with something apparently simple like handedness, there are possible confounding factors. For example, left-handed and ambidextrous people have a lower risk of brain cancer, perhaps because they zap their brain with cell phones more evenly across both sides, reducing the risk that a single DNA strand will be zapped one too many times, but they also earn more. I’ve written about handling multiple potential causes at the same time a few years ago.

The authors also point out that people might be inclined to blame it all on the phones and to report phone use on the side where the tumor was identified. This could be resolved if the controls are led to think that they have a tumor too, or if instead of asking how the phone is held, the interviewers instead made a call and observed the subject, or asked about a value neutral attribute such as handedness. Still, even in papers that reject the influence of phones on brain tumors, it’s always the case that more tumors are on the right side, just as we know that more people are right-handed than left-handed.

In the light of this investigation, I fully agree with Prof. Erikson that there is something going on.

The table in question is here: