sealPurdue News

February 1997

Effectiveness of warnings may depend on user, expert says

WEST LAFAYETTE, Ind. -- Why don't people heed warnings on products such as alcohol, glue and cigarettes? The answer has to do with how people weigh benefits vs. risks when making a decision, says a Purdue University expert on warning label design.

"If someone perceives a benefit in not following a certain safety rule or warning, they are likely to violate the rule or disregard the warning," says Mark Lehto, associate professor of industrial engineering.

In one study, Lehto found only one out of 54 subjects heeded the warning on a glue label to ventilate the room while using the product, despite the glue's foul odor.

"This study suggests that if someone's main goal is to complete a task, the benefits he perceives in finishing may outweigh the risks of skipping a safety step," Lehto explains. "Similarly, if someone's out to have a good time, the benefits he sees in having fun may outweigh the risks he sees in driving drunk. If you want people to behave more safely, you need something more dramatic than a warning label."

Increasing numbers of product liability lawsuits point to a need for improved criteria for deciding when and how to provide warnings, Lehto says. He has spent much of his career developing national and international guidelines for making warnings more effective.

For example, Lehto says responsible-drinking ad campaigns might be more effective if they emphasized the benefits of not drinking and characterized nondrinkers as more attractive or cooler than drinkers.

Products that emit warnings, such as smoke detectors, also could be made more effective if they took advantage of individual preferences, Lehto says. He is looking into a relatively new concept -- adaptive warning systems -- that may better meet the individual behavior patterns of a user.

"If a warning system such as a smoke detector is too sensitive, it will almost always detect a problem -- but it will also give off a lot of false alarms," Lehto explains. "After a while, some people won't pay attention to it any more and might react by turning it off completely, which isn't safe." With an adaptive smoke detector, individuals could adjust the device to be very sensitive or not-so-sensitive, depending on their preferences and lifestyles, he says.

Lehto and his colleague Jason Papastavrou, assistant professor of industrial engineering, are conducting experiments to determine whether people can adjust an adaptive warning system to their own behavior and sensitivity without jeopardizing safety.

CONTACT: Lehto, (765) 494-5428; e-mail,

Purdue News Service: (765) 494-2096; e-mail,

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