A taxonomy of behavioural interventions
A taxonomy of behavioural interventions∗ Christopher James Sampson November 7, 2014 Back in March I made a note to myself to write a paper — or, more likely, a blog post — presenting a taxonomy of behavioural interventions. I had gotten tired of everything being called a ‘nudge’ and with debates about whether nudges are ethical [1]. I even bought a copy of Nudge so that I could use it to populate the taxonomy with examples [2]. Thankfully, someone else was already working on this and has beaten me to it – producing almost exactly what I had in mind. Mira Fischer from the University of Cologne and Sebastian Lotz from Stanford have written a working paper titled ‘Is soft paternalism ethically legitimate? – the relevance of psychological processes for the assessment of nudge-based policies’ [3]. They differentiate between 4 types of behavioural intervention — or ‘nudge’ — and discuss the ethical implications associated with each by considering the psychological processes at play. It’s far better than any blog post I could have written, and I recommend reading it.
Fischer and Lotz’s taxonomy Consider a utility-maximising individual with 2 choices (A or B), each with 2 possible outcomes (1 and 2), such that the utility associated with choice A would be: UA = πA1 (uA1M + uA1N ) + πA2 (uA2M + uA2N )
(1)
where ‘π’ is the probability and ‘u’ the utility of the outcome and the ‘M ’ and ‘N ’ refers to monetary and non-monetary utility. Based on this, the authors then discuss the ways in which various types of nudge might influence the individual’s choice. Table 1 shows my interpretation of Fischer and Lotz’s taxonomy.
Is the taxonomy complete and well-defined? In my opinion, it is not. I do not believe that Type 4 nudges exist in the way described. The authors use the example of changing road markings to make drivers think they are travelling faster than they actually are and thus reduce their speed. It seems clear to me that this is an example of Type 2; the driver has been made to believe that the probability of them crashing at their current speed is greater than they would otherwise have believed. The idea that there is an ethical difference between nudges to our ‘automatic’ behaviour and nudges to our considered behaviour — given that so much of our behaviour is automatic — I believe is unfounded. When I was considering writing my own taxonomy of behavioural interventions, I was approaching it from a decision analysis perspective. Simply imagining the structure of an ∗
This blog post was originally published 30th May 2014 at http://aheblog.com/2014/05/30/ a-taxonomy-of-behavioural-interventions
1
Type Name
Point of influence
1
‘discomfort nudge’
choice evaluation
2
‘probability nudge’ ‘indifference nudge’
choice evaluation
‘automatism nudges’
?
3
4
Means of impact on Examples expected utility of choice non-monetary utility default settings on electronic devices; communication of social norms subjective probability informational camof realisation paigns monetary or non- positioning of monetary utility health/unhealthy products ? changes in road markings
preference formation
Table 1: Fischer and Lotz’s taxonomy individual’s decision process and considering the different points at which an individual could be influenced. Based on the Thaler/Sunstein definition, a nudge can affect any part of a person’s decision process; shown in Figure 1.
Figure 1: Decision process structure Based on this I believe there are 3 points of influence: i) before an individual’s preferences are defined ii) after the definition of preferences but before the observation of the choice set and iii) once the choice set has been recognised. Once preferences are defined and the choice set has been recognised there are 2 means of influencing choice; utility or probability. As such, I think the taxonomy should take the form shown in Table 2. Type Point of influence
A B
preference formation choice set observation
C D
choice evaluation choice evaluation
Means of impact on expected utility of choice values / priorities choice set expansion / compression subjective probability utility
Examples
education; positioning of food positioning of food; introduction of cycle lanes informational campaigns defaults; communication of social norms
Table 2: My taxonomy As the authors outline in their paper, particular nudges will cross type boundaries. I have included the ‘positioning of food’ nudge under 2 types to highlight this. If positioning causes an 2
individual to choose a healthy item — where they otherwise would have chosen a less healthy one — this could either be because they saw the healthy item first or because they simply didn’t see and fully consider the unhealthy option. In the former case Type A is at work, while in the latter case Type B is at work. I believe that educational interventions could fall into any of the above types because they can improve an individual’s ability to satisfy their own preferences. Type D could, of course, include a tax or subsidy. Furthermore, the ethical implications may be different depending on whether the impact on Type B, C or D is positive of negative, and also whether the impact on utility is monetary or non-monetary, which would increase the total number of types to 9. I don’t know whether I or the authors are either right or wrong, but there’s one thing we can agree on. One nudge isn’t necessarily as ethical as the next, so we need better ways of defining behavioural interventions.
References [1] The London School of Economics and Political Science. The Ethics of ’Nudge’ [Audio podcast]. 2014. [2] C. R. Sunstein and R. H. Thaler. Nudge: Improving Decisions About Health, Wealth and Happiness. Penguin, 2009. [3] M. Fischer and S. Lotz. “Is Soft Paternalism Ethically Legitimate?-The Relevance of Psychological Processes for the Assessment of Nudge-Based Policies”. http://ideas.repec. org/p/cgr/cgsser/05-02.html. 2014.
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Fischer and Lotz’s taxonomy Consider a utility-maximising individual with 2 choices (A or B), each with 2 possible outcomes (1 and 2), such that the utility associated with choice A would be: UA = πA1 (uA1M + uA1N ) + πA2 (uA2M + uA2N )
(1)
where ‘π’ is the probability and ‘u’ the utility of the outcome and the ‘M ’ and ‘N ’ refers to monetary and non-monetary utility. Based on this, the authors then discuss the ways in which various types of nudge might influence the individual’s choice. Table 1 shows my interpretation of Fischer and Lotz’s taxonomy.
Is the taxonomy complete and well-defined? In my opinion, it is not. I do not believe that Type 4 nudges exist in the way described. The authors use the example of changing road markings to make drivers think they are travelling faster than they actually are and thus reduce their speed. It seems clear to me that this is an example of Type 2; the driver has been made to believe that the probability of them crashing at their current speed is greater than they would otherwise have believed. The idea that there is an ethical difference between nudges to our ‘automatic’ behaviour and nudges to our considered behaviour — given that so much of our behaviour is automatic — I believe is unfounded. When I was considering writing my own taxonomy of behavioural interventions, I was approaching it from a decision analysis perspective. Simply imagining the structure of an ∗
This blog post was originally published 30th May 2014 at http://aheblog.com/2014/05/30/ a-taxonomy-of-behavioural-interventions
1
Type Name
Point of influence
1
‘discomfort nudge’
choice evaluation
2
‘probability nudge’ ‘indifference nudge’
choice evaluation
‘automatism nudges’
?
3
4
Means of impact on Examples expected utility of choice non-monetary utility default settings on electronic devices; communication of social norms subjective probability informational camof realisation paigns monetary or non- positioning of monetary utility health/unhealthy products ? changes in road markings
preference formation
Table 1: Fischer and Lotz’s taxonomy individual’s decision process and considering the different points at which an individual could be influenced. Based on the Thaler/Sunstein definition, a nudge can affect any part of a person’s decision process; shown in Figure 1.
Figure 1: Decision process structure Based on this I believe there are 3 points of influence: i) before an individual’s preferences are defined ii) after the definition of preferences but before the observation of the choice set and iii) once the choice set has been recognised. Once preferences are defined and the choice set has been recognised there are 2 means of influencing choice; utility or probability. As such, I think the taxonomy should take the form shown in Table 2. Type Point of influence
A B
preference formation choice set observation
C D
choice evaluation choice evaluation
Means of impact on expected utility of choice values / priorities choice set expansion / compression subjective probability utility
Examples
education; positioning of food positioning of food; introduction of cycle lanes informational campaigns defaults; communication of social norms
Table 2: My taxonomy As the authors outline in their paper, particular nudges will cross type boundaries. I have included the ‘positioning of food’ nudge under 2 types to highlight this. If positioning causes an 2
individual to choose a healthy item — where they otherwise would have chosen a less healthy one — this could either be because they saw the healthy item first or because they simply didn’t see and fully consider the unhealthy option. In the former case Type A is at work, while in the latter case Type B is at work. I believe that educational interventions could fall into any of the above types because they can improve an individual’s ability to satisfy their own preferences. Type D could, of course, include a tax or subsidy. Furthermore, the ethical implications may be different depending on whether the impact on Type B, C or D is positive of negative, and also whether the impact on utility is monetary or non-monetary, which would increase the total number of types to 9. I don’t know whether I or the authors are either right or wrong, but there’s one thing we can agree on. One nudge isn’t necessarily as ethical as the next, so we need better ways of defining behavioural interventions.
References [1] The London School of Economics and Political Science. The Ethics of ’Nudge’ [Audio podcast]. 2014. [2] C. R. Sunstein and R. H. Thaler. Nudge: Improving Decisions About Health, Wealth and Happiness. Penguin, 2009. [3] M. Fischer and S. Lotz. “Is Soft Paternalism Ethically Legitimate?-The Relevance of Psychological Processes for the Assessment of Nudge-Based Policies”. http://ideas.repec. org/p/cgr/cgsser/05-02.html. 2014.
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