So why does this happen? Sometimes it’s simply because the bigger, scarier number makes for a better story. In April 2004, a Boston Globe story reported that the risk of dying on the job in Massachusetts rose 65 percent in the previous year. That’s the relative increase, and it sounds dramatic. The story, headlined “Mass. workplace deaths rose last year,” got great play, at the top of the front page of the Metro Section. But the story failed to note that the big percentage (relative) increase meant that instead of fifteen out of every million workers dying on the job, the absolute risk rose only to twenty-five in a million. Pretty small. Not as good a story.

The UCS analysis illustrates another big reason why both risk numbers aren’t included. Few journalists understand the difference, and fewer still realize the importance of including both. So they simply never ask, which makes them vulnerable to the spin of advocates who selectively play up whichever number strengthens their case, and play down or leave out the number that weakens their case, as the UCS press release did.

I know the journalists involved in coverage of the UCS analysis at PRI’s The World and they are competent, fair professionals for whom I have a great deal of respect. But when they interviewed the UCS scientist who did the analysis, they simply never asked about the relative risk number. I made the same mistake all the time back in my reporting days. I just didn’t understand this critical part of risk until I joined the Center for Risk Analysis at the Harvard School of Public Health.

Absolute and relative risk are part of the basic “Who, What, When, Where, Why, How” questions that any story about risk should answer, which most journalists don’t know to ask because few are trained in these specifics. I’ve written about many others in a previous post. I’d have been a better reporter had I known them back then. They’re offered here in the hopes of making journalism a little better, and helping the public make more informed intelligent choices about the risky world in which we live.

Potential conflict of interest disclaimer: I have consulted to several clients in the nuclear field about the need to communicate more openly and honestly; the International Atomic Energy Agency, the Swedish Nuclear Authority, the National Radiological Emergency Preparedness Association, and the Nuclear Energy Institute.

David Ropeik is an instructor in the Harvard University Extension School's Environmental Management Program, author of How Risky Is it, Really? Why Our Fears Don't Always Match the Facts, creator of the in-house newsroom training program "Media Coverage of Risk," and a consultant in risk communication. He was an environment reporter in Boston for twenty-two years and a board member of the Society of Environmental Journalists for nine years.