How we judge decisions after the event

That is the conclusion of research by Dr Hartmut Blank from the University of Portsmouth and Birk Diedenhofen and Professor Jochen Musch from the University of Düsseldorf published in the British Journal of Social Psychology.

Why does research maintain that basing judgements on such reasons is problematic? This relates to two kinds of bias that affect human judgement:

· hindsight bias, where people overestimate the foreseeability and inevitability of outcomes after the event;

· outcome bias, where someone's behaviour, performance or decisions are judged in the light of a later outcome, even though that outcome may have been determined by other factors

To study these two kinds of bias, the researchers asked 282 people (123 from the UK and 159 from Germany), via an online questionnaire, whether the games had been a success or a failure and how foreseeable they thought this outcome had been. They also asked the participants whether the decision to award the games to London, which was made in 2005, was a good one.

What interested the researchers most was how far hindsight bias and outcome bias affected the participants' judgements of the decision to award the games and whether these effects were independent or not. Previous research had often treated the two biases interchangeably, so it was important to clarify their relation.

Across the UK and German samples, both hindsight bias and outcome bias affected the evaluation of the IOC decision, but the outcome bias effect happened to be stronger. A, say, 50 per cent increment in the perceived success of the Games led to a 30 per cent better decision evaluation, whereas a 50 per cent increment in perceived foreseeability inflated the evaluation by only 10 per cent.

Nevertheless, both effects were statistically significant, and most importantly they both directly and independently affected the decision evaluation, confirming the separate nature of the two biases.

Hartmut Blank said: "The main message of our study is that both outcome bias and hindsight bias can make independent contributions to the evaluation of decisions. Our respondents' evaluations of the IOC decision to choose London as the host of the 2012 Olympics depended both on how big a success they felt the Games had been and on how foreseeable a positive outcome was for them."

The researchers emphasise, however, that the strength and relation of the two effects likely depends on circumstances and should be followed up in future research. The current findings are 'proof of existence' of independent outcome bias and hindsight bias effects and a stepping stone toward more elaborate research involving the two biases.