The battle of the Nudge

I was invited to present a paper in Stirling, the European Capital of Nudge, last week. (

Here are pictures of me resisting the nudge to put my trash in the bin (pics taken by Leonhard Lades, my very nice host there).

I will not budge!
I will not budge!

This is actually a nice illustration of an issue with nudges, how they can make you do the opposite of what the nudger wants, just to mock the authority (or is that just me?).

Beyond having fun littering in the city, I also presented the results of a project that I did with the very clever, fast and efficient Magdalena Kaczmarek during the dying days of the Max Planck Institute of Economics in Jena.

We were investigating what happens after the nudge, i.e. the impact of nudges on people’s attitudes towards the behavior they are encouraged to adopt. Our question was whether the nudge changes people‘s mind about the “desirable action”, or if they rather react to it mechanically, like one reacts to an obstacle in the way of one’s preferences.

In our experiment, we offered people a total of 4€ to fill a survey. At the end, they could pledge the money to a charity. There were four treatments:

– Nudge: The default was to pledge to one charity.
– No nudge: The default was to keep money to oneself
– Nudge with choice: The default was to pledge to one of three charities.
– No nudge with choice: The default was to keep money to oneself, the alternative was to pledge to one of three charities

Taking the alternative involved a (limited) effort, i.e. writing “I want to do this” rather than clicking on a button to do what the nudge suggested.

In all cases, whether people pledged the money or wanted it for themselves, they had to come collect the money in our offices. They could then put the money into piggybanks for each charities.

Piggy Banks

We found that the nudge did work in eliciting about twice more pledges to charities. However, those who were nudged to pledge were less likely to actually come to claim the money. In the end, treatments with nudges did not result in more money actually contributed to charities.

We also elicited people’s attitudes to the charities and to us, the nudgers. We found that there was no apparent effect of nudges on people’s perception of charities, or of us, the nudgers. The good thing is that they did not make people more cross against charities or against us, so people do not usually react like me when people try to push me to do something.

In fact, the only robust effect on perceptions of charities was that if you give people the possibility to pledge, then they become less keen on charities than in a control treatment where they did not have the possibility to pledge. This is probably due to reactance, i.e. people trying to find reasons not to pledge by devaluing charities.

Giving more choice whom to pledge to improved matters only in so far as people were then more satisfied with their choices, but they did not pledge or contribute more, and giving choice did not improve their perception of us, the nudgers.

Subjects were not very fond of the possibility to contribute the money to a charity and were not keen on the possibility to donate proceeds from experiments in further experiments. Nudging them to pledge also made them more likely to say they felt forced to contribute.

Our experiment confirms the view that nudges act in a mechanical way, i.e. they lower the threshold at which people adopt a given behavior. We were able to exclude the other possible effect of a nudge, i.e. that nudging people to pledge makes them keener on charities. This could have been the case if people rationalize their nudged pledge ex-post by telling themselves they liked the charities. Instead, we found that nudges had no effect on people’s perceptions of the charities.

Change in attitude

Change in threshold

All this means that those who are nudged to do something will not keep on doing this in the absence of a nudge. We knew this already, but it also means that nudging people to do something that will require subsequent effort is unlikely to work if that subsequent effort is not also incentivized. Indeed, for our case, the people we nudged to pledge were “at the margin”, i.e. more or less indifferent between keeping the money or contributing it. This means that they were not so keen on contributing in the first place and were therefore unlikely to actually do the effort to collect the money in order to give it to charity.

As in the proverb, “there’s many a slip ‘twixt the cup and the lip”: getting people to “fake it” (pledge) does not always work to get them to “make it” (contribute).

Of course, charity muggers probably knew this already. You have to make sure to be ready to collect the money right then and there and you should not let people get away with just making a pledge.


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