Why there is no scientific consensus on the “nudge” 

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. 

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. 

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.

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 “1^st, 2^nd and 3^rd 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