What brings about social change? Sometimes, one cascading event brings a sweeping transformation in its wake – one person speaks up, and suddenly a chorus of voices joins in.


Often, though, it’s a lot subtler than that. Policies can be delicately tailored to encourage you to act in a certain way. Whether it’s a default rule, such as the NHS’s opt-out system for organ donation coming in 2020, a graphic warning like those on cigarette packets, or highlighting what most people do to encourage you to do the same, these subtle pushes are known as nudges.

In the following extract from his book How Change Happens (£24.00, MIT Press), Cass R Sunstein describes 10 of these nudges and explains how we encounter them in everyday life.

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10 Important Nudges

Nudges span an exceedingly wide range, and their number and variety are constantly growing. Here is a catalogue of ten important nudges — very possibly, the most important for purposes of policy — along with a few explanatory comments.


Default rules

(e.g., automatic enrollment in programs, including education, health, savings)

Default rules may well be the most effective nudges. If people are automatically enrolled in retirement plans, their savings can increase significantly. Automatic enrollment in health care plans or in programs designed to improve health can have significant effects. Default rules of various sorts (say, double-sided printing) can promote environmental protection.

Note that unless active choosing (also a nudge) is involved, some kind of default rule is essentially inevitable, and hence it is a mistake to object to default rules as such. True, it might make sense to ask people to make an active choice, rather than relying on a default rule. But in many contexts, default rules are indispensable, because it is too burdensome and time-consuming to require people to choose.



(in part to promote take-up of existing programs)

In both rich and poor countries, complexity is a serious problem, in part because it causes confusion (and potentially violations of the law), in part because it can increase expense (potentially reducing economic growth), and in part because it deters participation in important programs. Many programs fail, or succeed less than they might, because of undue complexity.

As a general rule, programs should be easily navigable, even intuitive. In many nations, simplification of forms and regulations should be a high priority. The effects of simplification are easy to underestimate. In many nations, the benefits of important programs (involving education, health, finance, poverty, and employment) are greatly reduced because of undue complexity.

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Uses of social norms

(emphasizing what most people do, e.g., “most people plan to vote” or “most people pay their taxes on time” or “nine out of ten hotel guests reuse their towels”)

One of the most effective nudges is to inform people that most others are engaged in certain behaviour. Such information often is most powerful when it is as local and specific as possible (“the overwhelming majority of people in your community pay their taxes on time”). Use of social norms can reduce criminal behaviour and also behaviour that is harmful whether or not it is criminal (such as alcohol abuse, smoking, and discrimination).

It is true that sometimes most or many people are engaging in undesirable behaviour. In such cases, it can be helpful to highlight not what most people actually do, but instead what most people think people should do (as in, “90 percent of people in Ireland believe that people should pay their taxes on time”).

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Increases in ease and convenience

(e.g., making low-cost options or healthy foods visible)

People often make the easy choice, and hence a good slogan is this: make it easy. If the goal is to encourage certain behaviour, reducing various barriers (including the time that it takes to understand what to do) often helps. Resistance to change is often a product not of disagreement or of skepticism, but of perceived difficulty — or of ambiguity. A supplemental point: If the easy choice is also fun, people are more likely to make it.



(e.g., the economic or environmental costs associated with energy use or the full cost of certain credit cards — or large amounts of data, as in the cases of data.gov and the Open Government Partnership; see opengovpartnership.org)

The American Supreme Court Justice Louis Brandeis said that “sunlight is said to be the best of disinfectants,” and disclosure can make both markets and governments much “cleaner.” For consumers, disclosure policies can be highly effective, at least if the information is both comprehensible and accessible. Simplicity is exceedingly important. (More detailed and fuller disclosure might be made available online for those who are interested in it.)

In some settings, disclosure can operate as a check on private or public inattention, negligence, incompetence, wrongdoing, and corruption. The Open Government Partnership, now involving dozens of nations, reflects a worldwide effort to use openness as a tool for promoting substantive reform; nations must produce national action plans containing new policies to increase transparency.


Warnings, graphic or otherwise

(as for cigarettes)

If serious risks are involved, the best nudge might be a private or public warning. Large fonts, bold letters, and bright colours can be effective in triggering people’s attention. A central point is that attention is a scarce resource, and warnings are attentive to that fact. One virtue of warnings is that they can counteract the natural human tendency toward unrealistic optimism and simultaneously increase the likelihood that people will pay attention to the long term.

There is a risk, however, that people will respond to warnings by discounting them (“I will be fine”), in which case it would make sense to experiment with more positive messages (e.g., providing some kind of reward for the preferred behaviour, even if the reward is nonmonetary, as in apps that offer simple counts and congratulations). Research also shows that people are far less likely to discount a warning when it is accompanied by a description of the concrete steps that people can take to reduce the relevant risk (“you can do X and Y to lower your risk”).


Eliciting implementation intentions

(“do you plan to vote?”)

People are more likely to engage in activity if someone elicits their implementation intentions. With respect to health-related behaviour, a simple question about future conduct (“do you plan to vaccinate your child?”) can have significant consequences. Emphasizing people’s identity can also be effective (“you are a voter, as your past practices suggest”).

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Precommitment strategies

(by which people commit to a certain course of action)

Often people have certain goals (e.g., to stop drinking or smoking, to engage in productive activity, or to save money), but their behaviour falls short of those goals. If people precommit to engaging in a certain action — such as a smoking cessation program — they are more likely to act in accordance with their goals. Notably, committing to a specific action at a precise future moment in time better motivates action and reduces procrastination.



(e.g., by email or text message, as for overdue bills and coming obligations or appointments)

People tend to have a great deal on their minds, and when they do not engage in certain conduct (e.g., paying bills, taking medicines, or making a doctor’s appointment), the reason might be some combination of inertia, procrastination, competing obligations, and simple forgetfulness. A reminder can have a significant impact.

For reminders, timing greatly matters; making sure that people can act immediately on the information is critical (especially in light of the occasional tendency to forgetfulness). A closely related approach is prompted choice, by which people are not required to choose but asked whether they want to choose (e.g., clean energy or a new energy provider, a privacy setting on their computer, or to be organ donors).


Informing people of the nature and consequences of their own past choices

(smart disclosure in the United States and the midata project in the United Kingdom)

Private and public institutions often have a great deal of information about people’s own past choices—for example, their expenditures on health care or on their electric bills. The problem is that individuals often lack that information. If people obtain it, their behaviour can shift, often making markets work better and saving a lot of money. If, for example, people are given information about how much they have spent on electricity in the last year, they can take steps to reduce their spending in the future.

How Change Happens by Cass R Sunstein is out now (£24.00, MIT Press)

How Change Happens by Cass R Sunstein is out now (£24.00, MIT Press)


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Sara RigbyOnline staff writer, BBC Science Focus

Sara is the online staff writer at BBC Science Focus. She has an MPhys in mathematical physics and loves all things space, dinosaurs and dogs.