A study by Filip Gesiarz, Donal Cahill and Tali Sharot of the University College London suggests people stop gathering evidence earlier when the data supports their desired conclusion than when it supports the conclusion they wish was false.
Previous studies had already provided some clues that people gather less information before reaching desirable beliefs. For example, people are more likely to seek a second medical opinion when the first diagnosis is grave. However, certain design limitations of those studies prevented a definitive conclusion and the reasons behind this bias were previously unknown. By fitting people’s behaviour to a mathematical model Gesiarz and colleagues were able to identify the reasons for this bias.
People start with an assumption that their favored conclusion is more likely true and weight each piece of evidence supporting it more than evidence opposing it. Because of that, people will find no need to gather additional information that could have revealed their conclusion to be false.
The study, “Evidence accumulation is biased by motivation: A computational account”, was published in PLOS Computational Biology.