The Power of Confirmation
Three scientists, Charles Lord, Lee Ross, and Mark Lepper, recruited forty-eight American undergraduates who either strongly supported the death penalty or strongly opposed it. They presented them with two scientific studies; one offered evidence regarding the effectiveness of capital punishment, and the other data showed its ineffectiveness. In reality, the studies had been fabricated. Lord, Ross, and Lepper had made them up, but the students did not know that. Did the students find the studies convincing? Did they believe that the data provided good evidence that should alter their minds? They did!
But only when the study reinforced their original view. Those students who strongly supported capital punishment thought the study that demonstrated its effectiveness was well conducted. At the same time, they argued that the other study was poorly executed and not compelling. Those who were originally against capital punishment assessed the studies the other way around. As a result, believers in the death penalty left the lab supporting capital punishment with more passion than ever, while those in opposition to it ended up opposing capital punishment with more zest than before.
Excerpt from: The Influential Mind: What the Brain Reveals About Our Power to Change Others by Tali Sharot