Cancer charities, radio shows, medical journals—they are all in the business of getting messages across to the public. If you can't capture the reader's or listener's interest, there is no way he or she will take in the important messages that you want to deliver. One way to grab that interest is to scare the audience rigid, but can it be justified?

The Imperial Cancer Research Fund is currently running a major advertising campaign that shows three little girls sitting on a wall. Over each head is a different label—teacher, lawyer, cancer. Meanwhile, in The Archers— Radio 4's long running soap opera of “everyday farming folk”—women's worst fears of breast cancer are exploited as an unfeasibly young character undergoes a mastectomy.

The cancer charity's campaign arose from a survey showing that the public thought an individual's lifetime risk of getting cancer was one in 10 or less. The “correct” risk is two in five. The charity then commissioned an advertising agency, Abbott Mead Vickers, to educate the public. Unfortunately, the advert creates the impression that only two of the three children will grow up to have a career. Alternatively, even if the third does grow up, her life will be defined …