Neither snap judgements nor sleeping on a problem are any better than conscious thinking for making complex decisions, according to new research that the researchers say debunks a controversial 2006 research result asserting that unconscious thought is superior for complex decisions, such as buying a house or car.

If anything, the new study suggests that conscious thought leads to better choices.

Since its publication two years ago by a Dutch research team in the journal Science, the earlier finding had been used to encourage decision-makers to make "snap" decisions (for example, in the best-selling book Blink, by Malcolm Gladwell) or to leave complex choices to the powers of unconscious thought ("Sleep on it", Dijksterhuis et al., Science, 2006).

But in the new study, to be published in The Quarterly Journal of Experimental Psychology, scientists ran four experiments in which participants were presented with complex decisions and asked to choose the best option immediately ("blink"), after a period of conscious deliberation ("think"), or after a period of distraction ("sleep on it"), which is claimed to encourage "unconscious thought processes".

In all experiments, there was some evidence that conscious deliberation can lead to better choices and little evidence for superiority of choices made "unconsciously". Faced with making decisions such as choosing a rental apartment and buying a car, most participants made choices predicted by their subjective preferences for certain attributes (for example, safety, security, colour or price), regardless of the mode of thinking employed.

Unconscious thought is claimed to be an active process during which information is organized, weighted, and integrated in an optimal fashion. Its benefits are argued to be strongest when a decision is complex - one with multiple options and attributes - because unconscious thought does not suffer from the capacity limitations that hobble conscious thought.

"Claims that we can make superior 'snap' decisions by trusting intuition or through the 'power' of unconscious thought have received a great deal of attention in the media," says University of New South Wales psychologist, Dr Ben Newell, lead author of the new study.

Among the headlines that followed the 2006 research are these: "Dilemma? Don't give it a thought," The Times, 17-02-06; "Trust your gut instinct when those shopping decisions get tough, say scientists," The Telegraph, UK, 17-02-06; "Big decision time? Best to sleep on it," Reuters News, 16-02-06.

"At best, these sorts of headlines are misleading," says Dr Newell. "At worst, they're outright dangerous. In stark contrast to claims made by the Dutch research team and in the media, we found very little evidence of the superiority of unconscious thought for complex decisions.

"On the contrary, our research suggests that unconscious thought is more susceptible to irrelevant factors, such as how recently information has been seen rather than how important it is. If conscious thinkers are given adequate time to encode material, or are allowed to consult material while they deliberate, their choices are at least as good as those made 'unconsciously'."