Within hours this summer, 30 American troops died in a strike in Afghanistan and millions of American investors watched the Dow Jones Average shed an astonishing 634 points in one day.

While it might be difficult to find similarities in the two events, social psychologists can detect a common theme: In each case, investments (money and human lives) were made, and those resources were painfully lost.

The 'sunk-cost' effect

Untold Americans experienced what is called the "sunk-cost" effect: Less a cognitive thought than an emotional one, this effect is the feeling that they are being wasteful if they terminate a prior commitment. Thus, they pondered: Stay the course and "waste not, want not"; or "cut and run."

Such a piercing event as suffering the greatest loss of American troops in the nearly 10-year-old war might seem to serve as a catalyst for people to denounce the war and demand a way out.

But a psychologist at Washington University in St. Louis, in what is thought to be the first non-anecdotal demonstration of the "activation" of the sunk-cost effect, has tested subjects and found that highlighting casualties prior to a questionnaire on both the Iraq and Afghanistan wars actually swayed people's pro-war attitudes rather than discouraged them.

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Study co-authors include Alan J. Lambert, PhD, Washington University associate professor of psychology in Arts & Sciences, and Washington University colleagues John Paul Schott and Laura D. Scherer, PhD.

Schott, a doctoral student in psychology, is the study's lead author. Scherer, a recent graduate of the university's doctoral program, is a postdoctoral fellow at the Center for Bioethics and Social Sciences in Medicine at the University of Michigan. The research team tested two groups each of approximately 85 students in 2007, on the Iraq War, and 2009, on the Afghanistan War.

Subjects were put into two groups. In one, they were asked to solve three decisions, all related to sunk-cost effects; in the other, they solved three different problems, not related to sunk costs.

In the former, one of the questions dealt with whether a subject would eat and finish an expensive lobster dinner even though it was not appealing because to not finish would be wasteful; in the latter, a subject's friend has flown in to visit and a choice must be made between going out to dinner, the friend's preference, or to a concert, the subject's.

Those participants exposed to the sunk-cost scenarios unknowingly were being primed to think of the aversiveness of throwing away previous investments, what Lambert calls "the don't-waste" goal.

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In Phase II of the experiment, all subjects were assigned one of two short reading assignments: One assignment was about war casualties, the other about the weather. Next, all subjects took an attitude questionnaire of 25 generic questions about the particular war.

Lambert and his group found that those subjects exposed to the don't-waste goal who read the story about war casualties tended to be significantly more in favor of the war than those controls who weren't primed the same way.

"The study shows that you can experimentally manipulate the salience of the don't-waste goal and if it's active in one context, choosing whether to eat the lobster, it also carries over into a completely different one -- people's appraisal of whether they want to commit to the Iraq or Afghan wars."

Lambert's findings will be published this fall in the Journal of Experimental Social Psychology.

Attitudes are malleable

Lambert is especially interested in people's attitudes, which he says are malleable and can be stretched like a rubber band either way, and the contextual factors that contribute to attitudes and decisions.

"We try to understand the situational factors that lead people to shift their opinions," he says. "People are notoriously bad at making assessments on when it's time to stop. They tend to be influenced by factors that they shouldn't be paying attention to, and probably the biggest of these is the psychological sense that they might be throwing away their investments. That's often a terrible basis for making the decision."

Whether they are consciously aware of it, people often base their decisions on an informal assessment of the costs and benefits of any choice, Lambert says. The problem, as noted by psychologist Robyn Dawes and others, is that people should be making assessments on the basis of future costs and benefits.

But that's not what people do.

Instead of looking forward, they look backward, and tend to make decisions in the service of justifying past expenditures that are "sunk" (irretrievable), no matter what they decide to do. That, said Lambert, is the core of the sunk-cost effect, in the sense that people are paying attention to resources that are already spent -- and, hence, should be ignored.

The sunk-cost effect occurs across situations, from investing, to expenditure of time, to relationships. In each case, investments can be sunk, "irretrievably no matter what your future decisions are," he says.

"Lives may be one of the more potent triggers of the sunk-cost effect. Money and relationships that are sunk are tough, too, but throwing away lives is deeply aversive, and such a powerful thing.

"The troops are dead and we can't get them back, but people still have this sense that they should continue their investment in the war to justify their deaths."

Formal study of the sunk-cost effect began about 50 years ago, first appearing in economics, but people long have been aware of the general "pull" of sunk costs, including Abraham Lincoln, who was fond of relating a saying his father told him: "When you make a bad bargain, hug it all the tighter."

While Lambert likes the Lincoln quote, he thinks it implies a free will that he thinks is lacking in the sunk-cost effect.

"I think of it as more of a feeling that you have to hold it closer, that the idea of letting go is so aversive," Lambert says.

The John Kerry moment?

People long have suspected that the tendency to justify the involvement in ongoing conflicts such as the Vietnam War was driven by the sunk-cost effect. However, the "evidence" for this idea is more anecdotal than empirical, Lambert says.

"What we've done is show that some of the more anecdotal views of human decision-making can be tested under controlled conditions," he says.

At what point, then, do people override the sunk-cost effect and experience the John Kerry moment?

Kerry, representing Vietnam Veterans Against the War, testified in April of 1971 before the Senate Foreign Relations Committee and asked: "How do you ask a man to be the last man to die for a mistake?"

Lambert said such a thing would be like "the antidote for the sunk-cost effect."

"I think in some way, you have to get people to look forward and make them aware that sunk cost is a gut feeling," he says. "You can either train them to not have the feeling that they're wasting resources or need to recoup their investment, or train them to not pay attention to the feeling.

"Our next direction may very well be the search for the antidote."