Narrator: This is Science Today. After years of scientific studies on the possible health risks associated with electromagnetic fields, or EMFs, the data is still inconclusive. But there does seem to be a low association between childhood leukemia and power line exposure. Richard Luben, a professor of biomedical sciences at the University of California, Riverside, says the public should understand just what "low association" means.

Luben: Just to put it in context, the level of risk that's associated with power lines, which is about a one point five fold increase in cancer, is about the same risk as associated with secondhand smoking.

Narrator: The key difference, Luben says, is literally millions more people are exposed to secondhand smoke compared to those exposed to power lines.

Luben: So, it's not only a matter of is there an effect, because I think people who responsibly look at the data will say that there is an effect there. There's also a question of how big the effect is how much risk is really there.

Narrator: For Science Today, I'm Larissa Branin.