Nudges, as characterized by Thaler and Sunstein (2008), aim to improve personal and societal welfare by steering our decision-making through insights from psychology and behavioral economics, without limiting freedom of choice. Nudges are designed to be easy and cheap to avoid. The nudge program is now global, with many governments adopting behavioral insights units in order to inform new social policies. So what’s the problem? Such an influential program of work has invited much debate, and so to push this into new directions this three-part series aims to communicate cutting edge insights on nudge, specifically concerning its evidential support, its theoretical basis, and its ethical acceptability.

The first part presented the foundations of the nudge programme in order to set up the second part of this piece which takes the form of a Q and A. In the second part three academics involved in the theory and practice of nudging describe their take on each of the three issues posed as questions to them. In this final part the aim is to summarize these answers and offer some ideas about how to move the nudge program ahead in ways that surmount some of the issues raised.

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Part Three

Building an evidence base: When it comes to assessing the effectiveness of a BCT, a practical solution offered by Weber is to have a publically accessible database of field trials that are being conducted globally. As all the contributors have indicated, a procedural assessment of BCTs is important, both for normative (Chater) and effectiveness evaluations (Grüne-Yanoff). Yet this requires prior procedural knowledge about the BCT. Could this actually be provided? The OECD has vast data-bases on ‘Social Protection and wellbeing’ (, under which a record of BCT applications could be included, and updated annually. As it is, most field studies, by necessity should record basic experimental details (e.g., when it was conducted, how long it was implemented for, number of participants, context, outcome measures, see Halpern, 2015). These details are necessary for a data-base for which fruitful analyses could help to answer questions such as ‘if it could be scaled-up, which BCT would work best to improve x behavior at a population level?’. Though, for a data-base of this kind to be useful, there has to be a willingness to be transparent in providing details of proposed trials before they are carried out, and making the results public, whether the trials succeed or not. This will require some political courage, but this is important if progress is to be made.


It is often the case in field studies that more than one BCT is employed to tackle a problem (Dombrowski et al, 2007). This level of transparency would enable researchers, policy makers, and practitioners to have a better grasp of the potential additive, multiplicative, or inhibitory effects (Berman & Johnson, 2015) of combinations of nudges used at any one time. It would also facilitate assessing their relative success vis-à-vis other interventions and/or common policy tools, or providing an appropriate baseline for RCTs.


Developing a psychological process based theory: The successful application of BCTs seem to involve the understanding and utilization of psychological theory, in particular the basic principles of human motivation and cognitive function. That is, we process magnitudes in relative rather than absolute terms, which matters for some BCTs (e.g., sizing of products, relative social comparisons – e.g., awareness of weekly alcohol consumption of peers) as discussed by Chater. Mental effort reduction can enhance the likelihood of making good decisions (Shah & Oppenheimer, 2008), which matters significantly for the effectiveness of automatic defaults, as discussed by Grüne-Yanoff and Weber. While it is possible to point to success stories of such as these, each expert’s response makes some cautionary points, which are worth summarizing here. First, what is needed is an a priori account of the specific causal (psychological) mechanism that is supposed to explain the effect sizes of BCTs observed in lab or field experiments. This is still an ongoing problem, and without an account of the psychological processes that underlie them, the nudge program, and others like it, are not going to progress towards understanding what interventions work when, where, on who, and for how long (Grüne-Yanoff, 2015). Second, basic cognitive functions determine behavior along with individual differences in, for example, value systems (cultural, social, political), and motivational attitudes towards changing behavior will play a significant role in determining the efficacy of certain types of BCTs (Osman, 2014; Saghai, in prep). Therefore, what is needed, is to go beyond a naïve assumption that one single factor is at work when psychology tells us that multiple factors usually underpin a single behavioral outcome (Ouellette, & Wood, 1998), and as emphasized by Weber. So, theory development of BCT effectiveness would do well to exploit this insight.


Ethics: There is a robust evidence base to suggest that life style choices, environmental conditions, and urbanization are highly predictive of chronic health problems, which in turn are associated with several severe mental health conditions (Tost et al., 2015). This makes for a compelling justification to continue work in targeting, through BCTs, poor lifestyle choices that contribute to mental and physical health problems. But as the experts in this essay have highlighted, meddling in the way people conduct their day to day lives raises ethical concerns, even if the meddling is seemingly benign. What are the solutions? One that is borne out of recent survey work (Sunstein, 2016b), is that people prefer to know about the BCT, rather than have them implemented in an opaque manner. To add to this, both Grüne-Yanoff and Chater share the view that ethical issues could be addressed by collective support for a BCT, through transparency, not only of the implementation of BCT themselves, but the rationale for them being used. On the view that choice behavior is not always a reliable way of exposing “true preferences”, Weber makes the point that collective support might also be assessed by looking at the fit between the outcomes of BCTs, that is, what people end up choosing to do, and tracing that back to what they actually want (by asking them), and looking at the correspondence of the two. The more closely aligned behavioral change is to preferred behavior, the more likely it is that the BCT is going to be endorsed, and the less likely it is to be viewed as a breach of autonomy (Osman, 2016).

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Nick Chater: Nick Chater joined Warwick Business School in 2010, after holding chairs in psychology at Warwick and UCL. He has over 200 publications, and was elected a Fellow of the Cognitive Science Society in 2010 and a Fellow of the British Academy in 2012. Nick is co-founder of the research consultancy Decision Technology; and is on the advisory board of the Behavioural Insight Team (BIT), popularly known as the ‘Nudge Unit’.


Yashar Saghai: Yashar Saghai is currently a research scholar and associate faculty member at the Berman Institute Johm Hopkins University. His research in applied ethics, political philosophy, and philosophy of science focuses on possible food futures. He engages with several fields, such as: food and agriculture; futures/foresight studies and history; public health and medical research; behavioral economics and cognitive psychology.


Elke Weber: Elke Weber is Gerhard R. Andlinger Professor Princeton University after holding the Jerome A. Chazen Professor of International Business in the Management Division of Columbia Business School and a chair in psychology. She has over 200 publications, is past president of the Society for Mathematical Psychology, the Society for Judgment and Decision Making, and sit on advisory committees of the U.S. National Academy of Sciences.


Till Grüne-Yanoff: Till Grüne-Yanoff is Professor of philosophy at the Royal Institute of Technology (KTH) in Stockholm. He has over 60 publications on the topics of philosophy of science and decision theory, as well as formal models of preference consistency and preference change, and the evaluation of evidence in policy decision making. He is a member of the TINT Finnish Centre of Excellence in the Philosophy of Social Science in Helsinki.


Magda Osman: Magda Osman is Associate Professor of Experimental Psychology at Queen Mary University of London. She has over 60 publications and authored 3 books. Her research interests include dynamic decision-making, agency and control, and critical evaluations of dual-systems of thought. She is head of the Centre for Mind in Society, and sits on various advisory panels, consulting on banking regulation, food safety, and advertising.