The fact that happiness and sadness spread through social circles like ripples in a pond was proven some time ago. It may take more than a year for a positive or negative feeling to make its way through related groups of friends, until the emotion finally has no more “stamina” left to move forward. Experts are fascinated with this mechanism, and a new field of science has emerged to study these interactions in particular. But a series of recent studies suggests something that previous researches never even hinted at, namely the fact that people can also catch another person's irrational processes and bad decisions. The find is of tremendous importance, ScienceNow reports.

One good example is a classic economic fallacy known as “sunk costs.” You buy a house by paying too much for it, a lot more than its actual worth. Then, rather than accepting that you have made a mistake, you keep pouring more and more money into the property, though deep inside you know that it's never going to sell for more than you paid for it. This doesn't stop you from trying to justify the original, bad investment with new ones. The new studies essentially show that this type of behavior can be contagious, which has considerable implications for the field of analyzing social interactions.

In a series of experiments, coordinated by Adam Galinsky, a social psychologist at the Northwestern University in Evanston, Illinois, two groups of students were asked to participate in a bidding game, and help a person that they had never met. They were not told that the person was fictitious. They all watched as the “person” put their money on the line for a virtual object, all on computer screens. Then, half of the students were told that they shared the same birth year, or the same birth month, with the fictitious character.

Normally, any sane person would have stopped the bidding when it became apparent that the bidder – the fictitious character – was throwing good money after bad. But 60 percent of those who were told that they had something in common with the bidder continued to bid as well. This could hint at the fact that people who feel connected to each other (families, close groups of friends, etc.) are very likely to repeat each others' mistakes, without necessarily realizing this. “I didn't realize just how easily linkages across decision-makers can be formed,” psychologist Barry Staw, from the University of California in Berkeley (UCB), who has not been involved in the study, concludes.