By Brian Carnell

Wednesday, May 21, 2003

Italian researchers published a study in "Human Reproduction" in April suggesting that men exposed to exhaust fumes from traffic had higher sperm motility than men not exposed to exhaust fumes. But the study is a classic example in the pitfalls of confounding factors.

Specifically, their study looked at men who worked at toll booths. Guess what men who work at toll booths do? They sit for up to six hours a day. Guess what one factor that can contribute to reduced sperm count is? That's right, prolonged sitting.

Now, the researchers claim they took this into account by using a control group that included clerks, students, doctors and drivers who have largely sedentary jobs that involve a lot of sitting. But unless toll booths in Italy include significantly different accommodations than toll booths here in the United States, six hours sitting at a toll both is not quite comparable to six hours of sitting in an office chair.

The study was also very small, involving an experimental group of 85 men and a control group of 85 men. None of which prevented the study from concluding based on their findings that, "Health authorities should be alert to the insidious health effects of environmental pollution."

A better lesson might be to avoid drawing such unwarranted conclusions from a single small study whose results are as likely explained by confounding factors as by the effects of pollution.

Sources:

Traffic pollution damages men's sperm. NewScientist.Com, April 30, 2003.

Traffic 'damages male fertility'. The BBC, April 30, 2003.

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