Imagine people randomly divided into two groups for a simple psychology experiment. Those assigned to one group are asked two questions. First, “Did Gandhi die before or after he reached the age of 140?” And then, “How old was Gandhi when he died?” Meanwhile, those in the other group are asked the same followup question, but their first question is “Did Gandhi die before or after he reached the age of 9?”

The results of actual studies just like this one are quite consistent and robust, and they may surprise you. Participants given “140 years” as their initial comparison point think that Gandhi lived much longer than those who were given “9 years” instead. Findings like these demonstrate what psychologists call the “anchoring effect”: our strong tendency to make judgments that are biased toward arbitrary standards of comparison. The plausibility of these comparison “anchors” makes no difference to us--we rely on them regardless. As another example, research subjects asked whether Einstein’s first visit to the United States occurred before or after 1992 give a much more recent estimate of when he arrived than those asked whether he visited before or after the year 1215.

This anchoring effect might be merely a perplexing curiosity--if not for its potentially profound consequences in the real world. Consider John McCain’s recent remarks that he’d be fine with American troops in Iraq for the next 100 years, or longer. Whether he’ll be able to implement the early steps of this troubling vision will depend on many things, including who’s sworn in as the next President of the United States in January 2009. But the “100 years” anchor can--on its own--shift the public’s expectations and comfort level for how long it’s reasonable to have troops in Iraq. Several additional years suddenly seems like a brief stay when compared to a century or more.