In the latest podcast I express my skepticism towards the nature of the Macbeth effect.The Macbeth effect is so named after Lady Macbeth, who, after murdering King Duncan attempts to wash the blood off her hands (both literally, and figuratively).

Spurred by this famous scene, the study found that washing one's hand after recalling or evaluating an unethical/immoral act seems to lesson one's guilt (Zhong & Liljenquist, 2006). A similiar and seperate study found that washing one's hands before making moral judgements seemed to minimize the degree to which one moralized on the topic (that is, they thought an act was less bad than they otherwise would have) (Schnall, Benton & Harvey, 2008)

In the podcast the examples centered around recalling one's own unethical act, then measuring if participants are washing their hands afterwards. Matt and James both questioned my skepticism (rightly so) and argue that doing the study with a bigger stimuli (say, exposing someone to a 40 minute documentary of the atrocities of WWII; or giving them the opportunity to actually steal, or commit an unethical act in situ ) wouldn't shed more light on the mechanism.

After much thought I've identified the source of my skepticism. I think there's a ceiling, and I think it's low.

The Macbeth effect is named after Lady Macbeth, who, after murdering King Duncan attempts to wash the blood off her hands (both literally, and figuratively). She finds, however, that it cannot be done. And this is my point - I think there's an upper limit, and I think this is important.

If a participant is asked to recall an unethical act (the best I could conjure is finding a wallet and keeping the money) they are 1) recalling an act from the past, which may be misremembered and misrepresented, and have 2) probably already engaged in extensive rationalizing of the event, such that any guilt or shame they feel has probably been extinguished some time ago.

So the brief recollection of an event, subject to the fallacies of memory and post-rationalizations, motivates people to clean themselves, or help a desperate PhD student.. With a trivial stimuli, you establish a trivial effect.

Get me to steal some money, make me feel personally responsible for the death of starving African children, make me feel real guilt and then measure the effect. Does washing one's hands relieve it? Does it relieve it to the same extent as it does for trivial stimuli? Does it relieve it proportional to the magnitude of one's own negative affect?

Additionally, perhaps washing one's hands works to relieve shame/guilt/responsibility at reliving an unethical act - but does volunteering to help a desperate PhD student? I argue in the podcast I don't see the link, why would volunteering relieve guilt? Here it seems trivial if the stimuli is more impactful - If I did feel responsible for the death of starving children I suspect I'd more likely want to recluse myself and sort it out in my head (or just attempt to ignore/forget it)... not stick around and do another experiment.

I do concede it's a provocative idea, and would very much like to know more, but when the stimuli lacks oomph, I suggest the effect itself can rightly be questioned. And given that the Macbeth effect is named after a failed example of the effect it purports to explain, I feel a little poetic justice in my skepticism

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Zhong CB, & Liljenquist K (2006). Washing away your sins: threatened morality and physical cleansing. Science (New York, N.Y.), 313 (5792), 1451-2 PMID: 16960010

Schnall, S., Benton, J., & Harvey, S. (2008). With a Clean Conscience: Cleanliness Reduces the Severity of Moral Judgments Psychological Science, 19 (12), 1219-1222 DOI: 10.1111/j.1467-9280.2008.02227.x