Quicksilver message: How to send a public health warning

When I was a smoker, I paid no attention to the constant health warnings about tobacco. It’s not that I was unaware that cigarettes posed serious risks. They were spelled out in black-and-white, right there on my pack of Camels. I just put them out of my mind—for future consideration.

I quit smoking long ago. The years have made me more averse to health risks in general, and I take precautions when I can. For example, I’ve seriously cut back on canned tuna in my diet, based on what I’ve read about mercury risks. The idea of quicksilver in my tuna fish sandwich makes me uneasy.

Mine are the kinds of decisions that drive public health officials crazy. My decision to smoke was based on denial and defensiveness. I refused to heed the message, even to see its relevance, though it was aimed directly at me, a committed smoker. My tuna decision may be just as irrational for different reasons. I may be wrongly generalizing an emotional public health appeal—one meant specifically to alarm pregnant women—and taking overzealous precautions as a result.

The ideal public health warning leads to a well-calibrated level of concern. People who are at high risk ought to respond strongly, but people at low risk should not react with alarm. How does one craft such an ideal message?

Psychological scientist Dale Griffin of the University of British Columbia has some thoughts about this tricky public health challenge. Working with Peter Harris of the University of Sheffield, Griffin has been exploring the surprising idea that a strong sense of personal identity might equip us for more nuanced reactions to health warnings. The theory is that affirming one’s sense of self and values diminishes both misplaced fear and defensiveness, leading to a more open-minded and measured response to threats—and only to relevant threats. Here’s how they tested this idea in an on-line experiment.

They wanted to study a real-world health issue, with real risks for some people and not for others. So they picked mercury in seafood, and they recruited a group of women of childbearing age who ate at least some fish and shellfish. They asked the women about their consumption of tuna—canned and fresh, including sushi—and this was used as a measure of the issue’s personal relevance for each of them. They also answered questions about psychological defensiveness. Defensiveness and personal relevance tend to combine in making people unresponsive to public health warnings—as with my smoking.

Then all the women wrote a short essay. Some wrote about the relevance of their most important values to their own lives—a prime intended to affirm their sense of personal integrity. The others wrote about less important values and how they might be relevant to others; these were the controls.

Afterward, all the women read a 2009 FDA brochure on mercury in seafood, which includes a recommendation that women limit their consumption of seafood (including tuna) before, during and right after pregnancy. Finally, they assessed the women’s responsiveness to this warning in a variety of ways, including how deeply they thought about the threat; the perceived relevance of the warning; their personal risk and their level of worry.

When they crunched all the data together, the findings were clear and striking. As reported in the on-line version of the journal Psychological Science, a simple act of self-affirmation reduced both kinds of decision making error. For women who ate a lot of seafood, self-affirmation increased concern and worry—but only for those who were defensive to begin with. It reduced concern and worry for those who were not as defensive—that is, for women who were not in denial about the real risks.

Just as important, self-affirmation actually diminished worry for those who didn’t eat a lot of fish—the very people who shouldn’t be worrying. In other words, having a strong sense of personal values improved the fit between individual women and the public health message, which allowed them to more finely calibrate their emotional responses.

This scenario is not entirely hypothetical. Not long ago, an appeals court in California affirmed that health warnings about mercury in tuna should not be posted in supermarkets. One argument against the posted warnings, which were aimed at pregnant women, was that they would stir up unfounded fears in people with nothing really to fear—and cause them to avoid a food with high nutritional value. This research could point the way to public health alerts that arouse just the right level of fear, in only the right people, and help others keep their health risks in perspective.

Wray Herbert’s book, On Second Thought: Outsmarting Your Mind’s Hard-Wired Habits, includes a chapter on heuristics and health risks. Excerpts from his two blogs—“We’re Only Human” and “Full Frontal Psychology”—appear regularly in Scientific American Mind and in The Huffington Post.