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Throughout the pandemic, many governments have had to rely on people doing the right thing to reduce the spread of the coronavirus—ranging from social distancing to handwashing. Many enlisted the help of psychologists for advice on how to "nudge" the public to do what was deemed appropriate.

Nudges have been around since the 1940s and originally were referred to as behavioral engineering. They are a set of techniques developed by psychologists to promote "better" behavior through interventions rather than "hard" ones (mandates, bans, fines). In other words, people aren't punished if they fail to follow them. The nudges are based on psychological and behavioral economic research into human behavior and cognition.

The nudges can involve subtle as well as obvious methods. Authorities may set a "better" choice, such as donating your organs, as a —so people have to opt out of a register rather than opt in. Or they could make a healthy option more attractive through .

But, despite the soft approach, many people aren't keen on being nudged. During the pandemic, for example, scientists to nudging in social and news media in the UK, and discovered that half of the sentiments expressed in social media posts were negative.

1. Nudges can be limited and fragile

Informational nudges were common during the pandemic. In response to such campaigns, people said they would wash their hands more—with a 7% increase in and a 2% boost in . In , such nudges increased people's willingness to wear a mask by 3%.

So much is made of the power of nudging because because large field studies, involving millions of people and conducted by government-funded behavioral change organizations, and . Even though the effects are small, when scaled to a population, one to two percentage point increases in positive effects on behavior may translate into thousands or even millions of changed minds (depending on the country). But this is similar to the level of effects that are achieved in psychological experiments using a . The effect sizes are also similar to (random irregularity in data) in scientific studies.

There is also work showing that when compared to hard interventions (for example, ) nudges deliver a lower overall benefit over time. Long-term studies into environmental nudges also show that nudge effects are feeble, and only work on those already motivated to be pro-environmental. Also, there are several moderating factors that help to explain the fleeting effects of nudging, such as , , and .

To be worthwhile, then, the of implementing nudges need to be outweighed by the benefits in behavioral change achieved. Moreover, in evaluting the costs and benefits, the effects of nudging need to be demonstrated to sustain over time, and as yet the jury is out on this.

2. Nudges can be unethical

Nudges may also present ethical concerns. For instance, nudging , dubbed "nudgeomics," meaning DNA is used to tailor nudges that can improve people's health. This is so new that there's little evidence to assess effectiveness. But using someone's DNA to try to manipulate their behavior may have implications for insurance purposes, for example.

Nudging may also be aided by artificial intelligence—so-called . Intelligent software algorithms can be used to influence people's behavior by targeting , and . We experience this in video games, news recommendation aggregation engines, fitness trackers and tailored advertising—which all try to influence us based on what they know about our behavior.

We have yet to tackle the basic concerns with the , let alone its expansion into areas with their own ethical issues such as and .

3. Nudges can backfire

Nudges can fail—and even . An environmental nudge removing bottled water to try to reduce plastic waste, for example, directly increased —resulting in a similar number of discarded bottles as before.

The failure rate of nudging , partly because of , which is not uncommon in psychology—typically only studies of successful nudges are submitted to .

So a lot of cherry picking may be going on. One way to address this is through pre-registering studies before they are run, though this isn't standard convention yet, .

4. Nudges lack theoretical backing

There are no comprehensive theories of . Instead, there are general frameworks that loosely connect work from psychology and behavioral economics to for using public policy interventions. Having a theory the psychological and contextual causal factors that account for the successes and failures of nudges.

The public should be more involved in discussions around the use of nudging so that everyone comes to a better understanding of the practical advantages balanced against honest communication of the scientific and ethical issues.

A resolute belief in something despite contrary evidence is nothing more than an act of faith those using behavioral change in public and private policy domains would do well to avoid. Ultimately, claims about the power of nudging need to be balanced against the obvious limitations that still need to be overcome.

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