When the captains of the nuclear industry originally offered the peanut butter equation, it didn't make them very popular with environmentalists and others who think we rely too heavily on half-tamed technologies and chemicals. The environmentalists, in fact, wanted to knock the captains of the nuclear industry down and stuff jelly up their noses.

But the peanut butter equation illustrates a point:

• Scientists rate nuclear power as fairly safe; lay people are horrified by it.
  
  
• Scientists think X-rays are moderately dangerous; lay people aren't so worried.
  
  
• Scientists rate swimming as rather hazardous; lay people consider it rather harmless.

Risk perception seems to attract scientists with a frisky approach to research.

Using these and more orthodox approaches, risk-perception researchers have identified some general rules that cause us to greet danger with a yelp or a yawn. As stated by Carnegie Mellon researcher Baruch Fischhoff, "We probably do have our priorities screwed up, but there's usually some reasonable reason for it."

• Natural risks are less scary. Perhaps this explains why we loathe nuclear power but ignore the radioactive threat of natural radon gas.
  
  
• Risks imposed on us seem worse. We can decide if we want to risk swimming, but when a hazardous waste incinerator sprouts next door we feel powerless and panicky.
  
  
• Risks with an obvious benefit are less daunting. One reason we give appreciative ratings to X-rays and surgery is that we focus on the payoff.
  
  
• Risks associated with complex technologies and catastrophes are greater. This is partly because the media dwell on catastrophes. If each day's headline read, "One in 50 of You Will Die in a Car Crash" (and this is an amazing, true fact), we'd think twice about risking our necks in those death traps every time we need a donut.

And that explains the big smile on my face every time I tempt fate by eating a peanut butter sandwich in the car on the way to the pool.