Does nudging really work? Let's look at the evidence.

The effects of nudging are probably much smaller and more situational than is often claimed, writes UNSW Business School’s Frederik Anseel

If you ever aimed at a fly in the urinal in an airport toilet, it was a nudge to pee cleaner. If you've ever shovelled fruit into a holiday buffet because it looked so good, it was a nudge to eat healthier. If you chose insurance for your rental car because it was standard in the package, it was a nudge to make a safe financial choice. If you followed a sign to take the stairs instead of the elevator, it was a nudge to move healthier.

Nudges are behavioural interventions that help you make healthier, financially better or more environmentally friendly choices. You will not be rewarded or punished for that choice. Merely changing the way the options are presented leads people to choose the right option. Usually, nudges are disappointingly trivial, like sending a reminder for a vaccination appointment.

In their 2008 bestseller, Nudge, Richard Thaler and Cass Sunstein gave the starting signal for the worldwide emergence of nudge units, small groups of behavioural scientists who help the government to solve social problems by designing nudges. Richard Thaler's Nobel Prize and Cass Sunstein's role in the Obama administration gave nudging stardom status around the world.

When teaching behavioural economics a couple of years ago, I asked my students to empirically test a well-known experiment or nudge again. The results were often distressing. Our students rarely succeeded in replicating the known effects from the literature. Around that time, we also heard more and more critical voices worldwide questioning the usefulness of nudging. COVID was a turning point. A number of behavioural scientists overplayed their hand trying to apply nudging to help fight the corona pandemic. The nudges they suggested to keep people at home, wear masks or keep their distance were often childishly naive and ineffective.

Is nudging really effective?

A scientific debate recently erupted about the effectiveness of nudging. A new meta-analysis, a statistical summary of all published studies, initially concluded that nudging interventions showed strong effects on choice behaviour. A series of reactions from fellow scientists took issue with that conclusion. First and foremost, such a meta-analysis is doomed to lead to silly conclusions. You lump all the data you find together, comparing apples and oranges, and then try to summarise the outcome in one single number. Nudges that focus on healthy eating thus end up in the same statistic as nudges intended to make people pay their taxes on time. It’s a nonsensical exercise.

But the main criticism was about the effect size produced by that meta-analysis. Their conclusion seemed to fly in the face of our accepted knowledge about the strength of psychological interventions in the real world. How is that possible? If it is just a sum of the effects of all studies, why wouldn’t that be credible? The problem is that the meta-analysis only summarised published studies. 

In a new analysis conducted by suspicious colleagues, it now appears that scientific journals almost exclusively published studies that showed a positive effect. This is called publication bias. Studies, such as those of our own psychology students, that do not find a positive result disappear in a drawer. Researchers censor themselves or journals refuse to publish null or negative findings. As a result, we have scientific literature that is distorted and cannot make any credible statement about the effectiveness of nudging.

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So should we do away nudging? Probably not. Another meta-study, which summarised all studies conducted by two known nudge units without publication bias, gives more promising results and suggests they might be useful after all. 

Probably the best conclusion is that asking general questions like “Does nudging work?” is meaningless. It depends on what choice of behaviour you are trying to influence. The effects of nudging may be smaller and more situational than is often claimed. That sounds less sexy than a psychological intervention that acquired stardom and made government headlines. It's time for modesty. Nudges are not a passe-partout for every policy problem.

Frederik Anseel is Professor of Management and Senior Deputy Dean (Research & Enterprise) at UNSW Business School. His research focuses on the motivational micro-foundations of how people contribute to organisational success. For more information, please contact Prof. Anseel directly. A version of this post was first published in De Tijd.