Causation is a central concern of science. In closed systems such as those found in Chemistry and Physics, this is generally not too difficult. In open systems such those that we work on (i.e., telecom use) it is a tremendously difficult problem because multiple factors are at work at the same time and interacting with each other and with the phenomenon we’re trying to establish the cause for. Medical research is well funded and systematic (even in developing countries medical research tends to be the best performing) and there are many lesson that can be drawn from it for social science. Esther Duflo’s and Abhijit Bannerjee’s work on randomized field trials is the best example. The systematic reviews that we are getting into are another.

In a previous post I referred to Siddhartha Mukherjee’s writings (that I would use in teaching method, if I was back in graduate teaching). Mukherjee has written again on the problems of identifying causes of cancer, comparing and contrasting the recent news items on cellphones and formaldehyde. The danger is much greater with formaldehyde and the science is clearer. Yet the fuss is about cellphones, not formaldehyde. Why?

The first challenge is scientific. It concerns the complexity of identifying new carcinogens, and the need for consistent standards for doing so. Take the purported link between cellphone radiation and brain cancer. This link is based largely on the so-called Interphone study. In Interphone, men and women with a variant of brain cancer (called glioma) were asked to recall their level of exposure to cellphone radiation. The results, at first glance, were provocative. Men and women who recalled moderate phone use seemed to have decreased rates of brain cancer compared to those who rarely used cellphones. In contrast, men and women with the highest usage seemed to have an increased rate of brain cancer.

But pivotal uncertainties remain. Trials like Interphone depend on the ability of subjects to recall their prior exposures. Such recollections can be surprisingly inconsistent. Indeed, when some subjects’ actual phone use was logged, there were broad discrepancies between actual and reported usage.

There are other difficulties. Despite a drastic increase in cellphone usage over the past decades, there has been no significant change in glioma cancer rates across the nation. Perhaps it is too early to judge, but the enormous increase in phone usage should have caused at least a minor blip in glioma rates over 20 years — but no such increase is apparent.

There are other difficulties. Despite a drastic increase in cellphone usage over the past decades, there has been no significant change in glioma cancer rates across the nation. Perhaps it is too early to judge, but the enormous increase in phone usage should have caused at least a minor blip in glioma rates over 20 years — but no such increase is apparent.

And finally, the kind of radiation emitted by cellphones — unlike the radiation emitted by X-rays or nuclear bombs — cannot directly damage DNA. X-rays and nuclear radiation possess the energy required to alter genes and thereby cause cancer. But the frequency of cellphone radiation is more than a million-fold lower. If cellphone radiation is causing cancer, it is doing so through a mechanism that defies our current understanding of carcinogenesis.

He then contrasts the fuss about cellphones with the case of formaldehyde.

The second challenge facing cancer control agencies is political. The formaldehyde case illustrates this. Unlike phone radiation, formaldehyde has a well-established mechanism to cause cancer: it is a strikingly reactive chemical that can directly attack DNA. Experiments performed in the 1970s demonstrated that the chemical causes cancer in mice and rats. Following this data, sophisticated trials showed that men and women exposed to formaldehyde — morticians, for instance — had higher rates of leukemia than unexposed people.