Effect Measure

As the flu pandemic ramped up with no vaccine in sight, attention turned to more prosaic things people might do to avoid infection. At the top of most lists was hand washing. I think hand washing is a good thing to do, although the evidence it does much against influenza specifically is weak or non-existent. Hand washing has been shown effective in some studies involving other respiratory viruses and intestinal pathogens, so even it doesn’t work for flu you gain something. And now it appears there are other effects of hand washing. Long a metaphor for having done with something, new research suggests it may be more than a metaphor:

Long a metaphor for the desire to distance oneself from immoral acts, hand washing doesn’t just wipe the conscience clean – it also changes how an individual regards a decision they have just made.

Lady Macbeth notwithstanding, the physical act of washing one’s hands is known to ease the guilt we feel about past unethical deeds. Now it seems that the act also removes our natural inclination to validate even trivial past decisions. (Wendy Zuckerman, New Scientist)

The validation of trivial decisions here involves ranking music CDs. Student subjects ranked 10 of them and then were asked to choose which of their fifth or sixth ranked ones they’d rather own. That’s the set-up. Presumably most people would decide to own their fifth ranked rather than sixth rank, but the difference was that this was now a decision, not a ranking. It’s apparently well known that after deciding something, it is a natural reaction to reinforce your decision by investing what you chose with even more positive qualities and what you rejected with more negative ones. The act of choosing also polarizes and hardens opinions.

It was at this point in the experiment that hand washing came in. Half of the 40 student subjects were asked to judge the quality of a liquid soap just by looking at it and half by using it to wash their hands with it. This was unrelated to the CD judging, but afterwards they were asked to rank the CDs again. Those who didn’t physically wash their hands exhibited the expected pattern of ranking the chosen CD higher in the ten than the one they rejected, pushing each up or down an average of two places. That’s a pretty big change. The students who physically washed their hands kept the same ranking. The post-choice polarization didn’t happen. The effect wasn’t limited to CDs. It was the same with jam preferences and it wasn’t limited to liquid soap. It also worked with hand antiseptics. Physical hand cleansing not only removed dirt and microbes but also the need to justify decisions.

There are two interesting aspects of this noted by the researchers, led by Spike Lee and Norbert Schwarz of the University of Michigan, writing in Science. The first is the more obvious one that some metaphors are not just metaphors. They may have a literal content. Sometimes a cigar really is just a cigar, as Sigmund said.

The other is more interesting: that seemingly irrelevant and trivial daily tasks might have a significant effect on how we see the world, in this case how we justify the choices we make.

You can find the article here: Lee, S. Schwarz N., “Washing Away Postdecisional Dissonance,” Science 7 May 2010: Vol. 328. no. 5979, p. 709. DOI: 10.1126/science.1186799

If you decide to read it, you might or might not wish to wash your hands afterward.


  1. #1 Hand Gel G
    May 10, 2010

    I couldn’t find a full version to read but this has interesting implications for medical professionals and the decision making they do; it suggests that the act of washing hands at the end of a consultation means that any decision that has been made is unlikely to be mulled over afterwards.

  2. #2 daedalus4u
    May 10, 2010

    This is interesting, but I suspect it relates to prior conditioning of the subjects. When one does a task that soils one’s hands, when the task is finished, one engages in hand washing. Cleaning, cooking, car repair, gardening, lab work, etc; for a great many tasks, once the task is finished the last step in the task is to clean-up by washing one’s hands. When the task is finished, there is no need to keep thinking about it, so the cognitive state at the finish of the task becomes fixed and less susceptible to unconscious modification.

    I would expect to see some of this same effect with taking off gloves and with putting things away, cleaning up dishes, and other actions that can signal the end of a generic task. I suspect it holds most strongly for tasks that are somewhat trivial and that can be put aside until later. Tasks that are more complex and which require ongoing cogitation are not put aside following cleanup.

    I suspect that health care workers using hand sanitizers after seeing a patient will not invoke as much of this kind of effect because using a hand sanitizer isn’t a sign that a task is finished. The task of seeing patients isn’t finished when hands are sanitized, it is just a transition from patient x to patient y.