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Why there is no scientific consensus on the “nudge” 

Daniel Priolo
Lecturer in Social Psychology at Université Paul-Valéry Montpellier 3
Emma Tieffenbach
PhD in ethics and specialist in the ethics of donation
Audrey Chabal
Audrey Chabal
Journalist and Author
Key takeaways
  • Nudges are suggestions that aim to influence and change people’s behaviour in a predictable way: the default option on a phone, for example.
  • There is no consensus on nudges in the scientific community: in addition to having varying definitions, their effectiveness is varied.
  • Ethical issues are paramount as the nudge involves questions about the boundary between autonomous – albeit influenced – choice and forced choice.
  • Politically, nudges are criticised for delaying the implementation of state measures.
  • While nudges can be useful, it is important to take a step back and not forget that other means exist to change population behaviour.

You may have nev­er realised it, but chances are you’ve already been influ­enced by a “nudge”. Accord­ing to the two the­o­rists behind the term, Richard Thaler and Cass Sun­stein, nudges are sug­ges­tions that aim to influ­ence and change people’s behav­iour in a pre­dictable way. This is done with­out pro­hibit­ing any option, with­out any real finan­cial incen­tive and with­out pro­vid­ing addi­tion­al information. 

What is a nudge?

A well-known exam­ple of a nudge is the lit­tle fly insert­ed in the uri­nals of the toi­lets at Ams­ter­dam air­port, which is said to have great­ly reduced the work­load of the clean­ers, as men using them “aim bet­ter” thanks to this sim­ple addi­tion. With this exam­ple, we can see that it is human beings who are the tar­get of nudges.  Peo­ple steeped in cog­ni­tive bias­es (accord­ing to the Kah­ne­man­ian par­a­digm in behav­iour­al eco­nom­ics) and sen­si­tive to social influ­ences, as opposed to oth­er par­a­digms such as the eco­log­i­cal ratio­nal­i­ty devel­oped by Gerd Gigeren­z­er. Indeed, accord­ing to both the­o­rists, nudges are aimed at “mere mor­tals” and not at the homo eco­nom­i­cusof clas­si­cal eco­nom­ic theory. 

How­ev­er, the term nudge is rather gener­ic, and it is dif­fi­cult to know what we are real­ly talk­ing about when using it. And there are still grey areas in the way it is char­ac­terised – not all authors agree on the def­i­n­i­tion. “Depend­ing on the inten­tions of the nudger or the con­for­mi­ty with the right deci­sion, we can find dif­fer­ent ter­mi­nolo­gies such as dark nudge or sludge,” explains Daniel Pri­o­lo. “All these notions were invent­ed after the demon­stra­tion of the effects of influ­ence in social psy­chol­o­gy and our cog­ni­tive bias­es in behav­iour­al economics.” 

There are still grey areas with­in its char­ac­ter­i­sa­tion, and not all authors agree on the same definition.

Some even dis­pute the cen­tral idea that the nudge should not be pro­hib­i­tive. Emma Tief­fen­bach, PhD in ethics and a spe­cial­ist in the ethics of giv­ing, who works main­ly on char­i­ta­ble nudges at the Uni­ver­si­ty of Gene­va, sug­gests that in some cas­es a ban can be under­stood as a nudge. “Local bans on smok­ing, for exam­ple at an air­port, can be seen as nudges,” she says. “If some­one real­ly wants to smoke, they can walk a hun­dred metres or so and go out­side to do so. The oppor­tu­ni­ty is not tak­en away, it just requires an extra effort on their part.”

Some clas­si­cal exam­ples of nudges include the default option (your phone set­tings, for exam­ple), forced inter­ven­tion to com­plete a process (when the bank’s ATM asks you to with­draw your card to get your notes) or eye-lev­el place­ment (when the “health­i­est” food is placed at eye lev­el). Nudge advo­cates say that all these tech­niques are sup­posed to make your life eas­i­er and guide you towards bet­ter choic­es – assum­ing they are effective. 

Criticisms of nudges

Mech­a­nisms and prac­tis­es of nudges are mixed. “To say that nudges are or are not effec­tive is a bit like say­ing that med­ica­tion works,” sug­gests Daniel Pri­o­lo. Indeed, the par­al­lel with med­i­cine is rel­e­vant because the effec­tive­ness of a drug always depends on the effect size of the inter­ven­tion, spe­cif­ic judge­ment cri­te­ria, a ben­e­fit-risk bal­ance, and a con­text. The same applies to nudges. 

Nev­er­the­less, there is cur­rent­ly no con­sen­sus on the effec­tive­ness of nudges. A recent meta-analy­sis pub­lished in the Pro­ceed­ing Nation­al Acad­e­my of Sci­ence1 sug­gest­ed their over­all effec­tive­ness… before being crit­i­cised by oth­er authors who claimed that this effec­tive­ness was no longer rel­e­vant when pub­li­ca­tion bias was con­sid­ered to adjust the results2.

In the sci­en­tif­ic com­mu­ni­ty there is as much enthu­si­asm regard­ing nudges as there is crit­i­cism. Giv­en their nor­ma­tive objec­tives, they are also wide­ly dis­cussed in the field of ethics and polit­i­cal sci­ence: what are the accept­able lim­its of their use? How can we tell the dif­fer­ence between a moral and an immoral nudge? Let’s imag­ine that a nudge is imple­ment­ed to make you choose a fruit sal­ad rather than a choco­late cake in the cafe­te­ria. Yet today you real­ly want­ed cake. You might think there’s a prob­lem here, how­ev­er Emma Tief­fen­bach does not. “Nudges are not eth­i­cal­ly prob­lem­at­ic if they make us act in accor­dance with our sec­ond-order pref­er­ences,” she says. 

Sec­ond-order pref­er­ences are all those things that we would pre­fer to do (the ‘fore­see­ing self’ accord­ing to Thaler and Sun­stein), but fail to do because of our first-order pref­er­ences that make us act in the oppo­site way (the ‘act­ing self’). In the­o­ry this makes sense, although in real­i­ty it is very dif­fi­cult to assess this con­for­mi­ty. “All we see in real­i­ty are peo­ple who appear to be influ­enced by nudges, but it is very dif­fi­cult to know whether they are act­ing in accor­dance with what either their sec­ond-order pref­er­ences or their good judg­ment would lead them to do,” warns Emma Tieffenbach.

On the oth­er hand, nudges are prob­lem­at­ic if they influ­ence indi­vid­u­als with­out respect­ing their auton­o­my. “Nudges do not exploit our delib­er­a­tive capac­i­ties but our cog­ni­tive or affec­tive bias­es, or our exag­ger­at­ed aver­sion to cer­tain emo­tions such as shame or guilt. And this can be eth­i­cal­ly prob­lem­at­ic,” says Emma Tief­fen­bach. This leads to debates among ethi­cists: some con­sid­er that the vio­la­tion of auton­o­my is suf­fi­cient to pro­hib­it the use of nudges, oth­ers sug­gest that the ben­e­fi­cial con­se­quences of nudges from a glob­al point of view jus­ti­fy their use. 

In the sci­en­tif­ic com­mu­ni­ty there is as much enthu­si­asm regard­ing nudges as there is criticism.

Some nudges may exploit people’s exces­sive aver­sion to cer­tain emo­tions, such as shame, embar­rass­ment, or guilt. For exam­ple, char­i­ty nudges most often exploit the desire to avoid the guilt asso­ci­at­ed with the option of keep­ing mon­ey to one­self. “In this case, the nudge acts on indi­vid­u­als by asso­ci­at­ing cer­tain options, for exam­ple, hav­ing a cig­a­rette in the smok­ing area of an air­port, often a glass room, under the poten­tial­ly con­de­scend­ing gaze of passers-by, with an expe­ri­ence of shame that could deter even the most addict­ed smok­er. What is prob­lem­at­ic is that the men­tal cost asso­ci­at­ed with the option to smoke may be no dif­fer­ent in inten­si­ty and dis­com­fort than that of a fine. In this case, it is ques­tion­able whether the free­dom to smoke is real­ly pre­served,” says Emma Tieffenbach.

Nudges and politics 

From a more polit­i­cal point of view, nudges are sub­ject to three main crit­i­cisms. They are sus­pect­ed of favour­ing the sta­tus quo; of delay­ing the imple­men­ta­tion of tru­ly effec­tive mea­sures at a sys­temic lev­el; and of allow­ing exces­sive blame to be placed on the indi­vid­ual. A recent review pub­lished in Behav­ioral and Brain Sci­ences lists these crit­i­cisms and gives sev­er­al con­crete exam­ples3

To illus­trate the prob­lem of the sta­tus quo, imag­ine a slum­lord in a devel­op­ing coun­try. He might claim that peo­ple are unhealthy because they do not fol­low hygiene rules or because their diet is unbal­anced. The nudge pol­i­cy could then be used to increase the use of soap or to choose bet­ter foods. How­ev­er, the real rea­son for the poor health of the pop­u­la­tion seems to be the gen­er­al liv­ing con­di­tions of these peo­ple, and it is a real social pol­i­cy towards hous­ing that will solve the afore­men­tioned problems.

With regard to the oth­er two issues, the exam­ple of green nudges, such as the roll-out of Linky smart meters to all house­holds in the coun­try in France, can be tak­en. Although the aim of green nudges here is to help cit­i­zens become more aware of their ener­gy con­sump­tion, some con­sid­er that they place much of the respon­si­bil­i­ty for ener­gy prob­lems on house­holds with­out ques­tion­ing the over­all ener­gy pol­i­cy. Nev­er­the­less, the gov­ern­ment seems to be aware of these prob­lems4, and crit­i­cis­es nudges for not allow­ing rad­i­cal changes in both behav­iour and systems.

How­ev­er, this does not pre­vent it from mak­ing fre­quent use of nudges. “The gov­ern­ment reg­u­lar­ly calls on the Direc­tion Inter­min­istérielle de la Trans­for­ma­tion Publique (DITP) and the behav­iour­al sci­ences depart­ment with­in it to pro­duce visu­al com­mu­ni­ca­tions and adver­tis­ing spots. This was notably the case dur­ing the Covid-19 pan­dem­ic,” attests jour­nal­ist Audrey Cha­bal, who pub­lished the inves­ti­ga­tion Souriez, vous êtes nudgé (Smile, you have been nudged) on the use of nudges dur­ing the pan­dem­ic. “But it was not only the DITP that was respon­si­ble for this. For exam­ple, the BVA research com­pa­ny hired by the gov­ern­ment sub­mit­ted the idea of using the ter­mi­nol­o­gy of “1st, 2nd and 3rd line jobs” to the gov­ern­ment in order to get peo­ple to accept the idea that some peo­ple could go out to work while oth­ers would remain work­ing from home.”

To sum up, nudges are very diverse tools with mixed effec­tive­ness and some­times prob­lem­at­ic con­se­quences. While there is cer­tain­ly a range of pos­si­bil­i­ties with­in which they can be use­ful, it is impor­tant to always take a step back and not for­get that oth­er levers exist to change the behav­iour of a population. 

Julien Hernandez

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