Wash your hands, wash away doubt

09 May 2010


Pontius Pilate is probably the most famous person to have washed his hands of a problem, but new research suggests that the act goes beyond just the metaphorical: scientists in the US have found that washing hands can alter the decisions we make about something subsequently!

Person washing his handsMichigan researchers Spike Lee and Norbert Schwarz, writing in Science, initially asked 40 undergraduates to take part in a "consumer survey" and browse through 30 CDs, selecting their favourite ten and ranking them in order of preference. They were then told that they could choose between either the fifth or sixth CD in their order and keep their selection as a reward for their cooperation.

But before they took their rewards they were first asked to also rate some soap; half the students were told just to look at the soap in the bottle, the other half were also asked to use it. They were then re-presented with the ten original CDs and asked to rank them again, including choosing which of the two they would prefer to keep. Incredibly, those who had not washed their hands clung vigorously to their original preferences, viewing the chosen CD as much more attractive than the one they'd rejected. But amongst the students who had meanwhile washed their hands, this effect evaporated alongside the soap, with the subjects showing much less of a preference for one CD over the other.

The researchers then replicated the result using a second experiment on the taste of jam! This time 85 students were shown pictures of four different fruit jams and asked to pick one from two offered jars as a reward for taking part. Then they were asked, ostensibly as part of a consumer survey, either to examine an antiseptic wipe, or to physically use the wipe, before indicating on a scale of 1 to 10, how tasty each of the two jams - the one they'd previously picked and the one they'd rejected - would taste.

The participants who didn't clean their hands expected their chosen jam to taste significantly nicer than the one they had previously rejected. But for subjects who used the wipe this difference went away.

These fascinating findings suggest that hand washing has impacts beyond just the moral domain. In some way it can erase the traces of previous decisions, preventing us from loading judgements to justify the choices we have made. So next time you're faced with a difficult decision, wash your hands to wash away your prior prejudices, before finally making up your mind!


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