How do you change the behaviour of the world?

We all know that changing our behaviour isn't easy – and changing the behaviour of others is even harder. Whether it's convincing someone to exercise more, quit smoking or follow a healthier diet, human habits are notoriously difficult to budge. An even greater challenge is how to change the behaviour of a population.

During the Covid-19 pandemic, this was perhaps the biggest job of all. In many ways, it's now clear that the pandemic was as much a behavioural emergency as it was a medical one: Whilst vaccines and treatments were being developed in record time, changes to how we live, work and interact were needed immediately. Governments were tasked with convincing billions of people to stay at home, to avoid seeing friends and family, to mask up, and to literally roll up their sleeves.

Nearly five years ago, in April 2020, just a few months into the pandemic, Jay van Bavel – a social psychologist at New York University – published a landmark paper aimed at helping those in power do just that. Bavel and colleagues' paper was influential as it made clear that governments couldn't rely solely on rules and regulations; they needed to motivate the public to follow them. 

In doing so, they proposed 19 behavioural principles – policies that were rooted in decades of psychological research and designed to help guide the public's response to the pandemic. Many of these principles were adopted by governments around the world, in the hope that psychology might help 'nudge' us, or even shove us, towards safer behaviours. These principles took many forms, from encouraging a shared sense of identity – 'we're all in this together' type thinking – to targeting fake news and misinformation.

These questions were especially important to my own research, on adolescent social development and mental health. Could we really get young people to stick to these restrictions? And to what extent were the huge social sacrifices being asked of young people worth it in the long run? These unknown questions were hugely important to understand and to collect data on, and to understand what policies worked and were worth implementing.

So, my interest was piqued, and it wasn't too long before I found myself in the unusual position of having first-hand experience of very different approaches to the behavioural principles in action…

Support for the claims

In March 2021, I left a rainy, locked-down London and took an eerily empty flight to Australia to start a research job in Sydney, which involved examining the impact of the pandemic on adolescent mental health. After spending two weeks in hotel quarantine, and a lot of questionable meals later, I was let out to a lockdown-free Sydney. However, Australia's strict border rules and their initial zero-Covid approach began to fail. Soon Sydney, and other parts of the country, enacted their own lockdowns and approaches to controlling the spread of the virus.

A year since I moved, and still in the throws of the pandemic, myself and several other psychological and behavioural scientists from around the world joined together to try and assess the impact of the claims made in the Bavel paper. Led by Kai Ruggeri – an expert in the behaviour of populations at Columbia University – we wanted to know if the claims made were based on evidence. And when put to the test, how well did these strategies impact real-world outcomes during the pandemic?

Our findings, which were published in 2023 in the journal Nature, found evidence in direct support of 16 of the claims made in the Bavel paper, which fell into a number of broad categories, including a sense of identity, trust and leadership, messaging and language, and misinformation.

What's important here, though, is that the evidence we found took many forms. It came in various degrees of quality. Some were more robust, more trustworthy, and that has wider implications for the impact Psychology can have – around public health emergencies, and more broadly.

A sense of identity

Early in the pandemic headlines such as 'Coronavirus means we really are, finally, all in this together' (taken from The Guardian in 2020), proliferated the media. The pandemic cultivated a shared experience, or as psychologists call it, a shared social identity. This is the idea that our sense of belonging to a group can powerfully shape our behaviour. Social identity theory suggests that when individuals see themselves as part of a collective with shared goals, they are more likely to act in ways that benefit the group.

In the case of the pandemic, social identity theory would predict that if Governments harnessed this 'we're all in this together' mentality the public would be more motivated to adhere to public health messages, mask-wearing, social distancing and vaccination. And many governments did indeed adopt messaging that focused on collective identity, urging citizens to 'protect each other' or 'do their part' to stop the spread of the virus. For example, in the UK the Department of Health and Social Care used the slogan 'Stay at home, save lives', running across TV, radio and social media.

When assessing the evidence for this approach, we found that most studies showed positive associations between collective identity and people's engagement in prosocial – Covid-safe – behaviours. However, the studies that existed were primarily based on surveys and controlled experiments, rather than real-world assessments where observable outcomes, such as actual changes in behaviour, could be measured. For example, most studies focused on people's intentions to act in ways that might benefit others. Studies did find that people who felt a stronger sense of national or community identity were more likely to report intentions to follow public health recommendations.

However, it's all well and good having these positive intentions, but we all know that our intentions don't always translate to actions. Nudging people to behave differently by making social comparisons has, though, been proven to be effective in several other areas. 

For example, in one trial from 2017, the Department of Health in Australia found that GPs were most likely to reduce the number of antibiotics they prescribed if sent a letter comparing their prescribing behaviour to their peers – to other GPs in their local area who were prescribing less. In the context of Covid-19, however, there was a lack of real-world studies exploring this nudging behaviour, leaving us to speculate on its impact as an effective strategy.

Trust and leadership

Although the evidence around collective identity was generally positive, it's also important to acknowledge that promoting this 'we're all in this together' thinking can sometimes backfire, especially among polarised or fragmented societies. Think the USA. This approach is, therefore, likely to work best when messages resonate across social and political divides. It also goes without saying that this approach can easily be undermined when leaders break their own rules, as we saw happen in the UK.

This raises the important issue of trust, in our leaders and trust in our scientists. We found evidence to support the view that identifying trusted sources (including politicians) to share public health messages would be effective. We also found evidence – although limited – that if leaders themselves promote the idea that cooperating is the right thing to do, and make it clear that others are already cooperating, people will more likely follow the rules.

Messaging and language

In contexts where political divides strongly influence health behaviour, highlighting consensus among leaders across the political spectrum has the potential to increase compliance with important public health measures. Evidence from controlled experiments suggests that bipartisan support – strong agreement between opposing political parties – was associated with greater public engagement in health messaging.  This idea of putting politics aside was also publicly urged by Tedros Ghebreyesus, the Director General of the WHO:

'This is not the one to use for politics. It's like playing with fire… Please work across party lines, across ideology, across beliefs, across any differences for that matter. We need to behave. That's how we can defeat this virus.'

In societies that prioritise individual freedom over communal security, enforcing restrictive measures poses significant challenges. For example, evidence suggests that adherence to collective health measures, like lockdowns and mask mandates, was lower in more individualistic countries. This points to the potential benefit of framing public health messaging in ways that resonate with individualistic values. For instance, highlighting 'freedom from disease' as a positive outcome of compliance might align better with the values of individual autonomy and personal choice in these societies, potentially improving adherence.

Interestingly, when we assessed the claim that public health messaging that focused on protecting others would be persuasive, we found no support for this. Indeed, observational studies in real-world contexts where messages highlighted either self-protection or the protection of others surprisingly did not, consistently, lead to behaviour change. One possible reason for this is the constantly shifting risk levels and frequent updates to public health recommendations, which may have left people struggling to adapt.

Misinformation

One of the most pervasive challenges during the pandemic was misinformation, intersecting with nearly every aspect of the public health response. False claims that the vaccines could alter your DNA or even contain a microchip were prevalent. This misinformation was perhaps most salient on social media, and companies such as TikTok claimed to take down over 250,000 videos for Covid-misinformation.

Our review of the evidence around 'inoculation' against misinformation – a psychological approach that involves exposing people to weakened forms of misinformation along with accurate information and rebuttals – revealed some of the most robust, positive findings. Both lab-based experiments and real-world studies supported the effectiveness of this approach, showing medium-sized positive effects in reducing susceptibility to conspiracy thinking, fake news, and other types of Covid-19-related misinformation. 

In particular, the spread of fake news had a significant impact on vaccine hesitancy. Survey data and correlational studies indicated that exposure to misinformation contributed to increased reluctance and refusal to vaccinate. These effects were especially pronounced within communities already sceptical of government interventions, underscoring the importance of building and maintaining public trust in leaders. Therefore, these findings suggest that effective public health strategies must not only communicate accurate information but also actively counteract misinformation to ensure the public's trust and compliance with health guidelines.

Cultures and contexts

Our findings showed that many studies made general claims without specifying exactly what they expected to find or offered vague advice that made it difficult for policymakers to act. In the future, we as psychologists and behavioural scientists, need to be clear about our hypotheses and to create ones that are specific enough to produce actionable policy outcomes. The pandemic has shown us that this is more challenging than it seems, especially when there are so many unknowns. 

Importantly, much of the evidence we assessed came from WEIRD samples – people who are Western, Educated, Industrialised, Rich, and Democratic. This means that findings often weren't applicable to the global south or other regions with vastly different social and economic contexts. Going forward we need to ensure our findings reflect diverse populations so that policy recommendations are relevant across cultures and contexts.

Interestingly, we also found that much of the behavioural research during the pandemic was focused on psychological constructs. Things like beliefs, identities and perceptions. There was less attention given to the real-life barriers people face. This led us to recommend that in the future, we take an 'inside-out and outside-in' approach. 

This is where we don't just focus on the psychology of compliance, but also look at structural factors like access to healthcare, the internet, and how legislation affects behaviour. People's choices aren't made in a vacuum: we know that they are shaped by their environment, and future policies need to reflect that.

Related to this, we need to be careful to avoid the 'streetlight effect': studying something just because it's easy to, but not what really matters. We need to go beyond relying on WEIRD samples, and online surveys. We need to study the people that are most affected by public health issues, and who would benefit most from interventions, not just those who respond to an online survey. 

And as with all areas of science, null results need to be taken seriously – highlighted, not swept under the rug. When we find that something might not work, it's crucial to recognise that and not keep throwing resources at it – especially when those resources we do have are so limited. For example, while hundreds of studies focused on promoting handwashing, the real impact came from interventions like masking and vaccination.

Beyond the pandemic

As much as behavioural science was used during the pandemic to guide policy decisions, what we've learnt from this also has the potential to tackle other pressing issues such as climate change or economic inequalities. With the example of climate change, tackling it will require not only scientific solutions but also a major shift in people's daily habits. Drawing on the evidence we evaluated from the pandemic, it's clear that behavioural science, and psychology more broadly, have the potential to guide the development of campaigns that would help lead people to make more sustainable choices and to make these choices feel desirable.

This approach also has the potential to transform how we deal with other issues of public health. Behavioural science could inform better strategies for managing other issues like obesity, substance abuse, or mental health. However, for these interventions to be effective they need to be rigorously tested and tailored to fit diverse communities: the research we evaluated rarely had a good grounding in real-world evidence. We also know from countless examples that one-size-fits-all approaches rarely work.

In short, our findings show that behavioural science offers the potential to inform policies across a range of issues important to us all – but such an approach should always be grounded in quality, representative research. That said, whilst behavioural science provided us with essential guidance, we cannot lose sight of the huge sacrifices we all made during the pandemic – the isolation, loss, and new ways of living. These experiences had vastly different impacts on each of us, some of which are still unknown.

Effective policymaking is, therefore, not just about data, but also about weighing up the impact that these policies have on each of us, for better or worse. And the challenge really comes when these impacts are hard, or even impossible, to quantify.

Dr Jack Andrews is a Wellcome Trust Early-Career Fellow in the Department of Experimental Psychology at the University of Oxford and a Stevenson Junior Research Fellow at University College, Oxford.

Key sources

Ruggeri, K., Stock, F., Haslam, S.A., et al. (2024). A synthesis of evidence for policy from behavioural science during COVID-19. Nature, 625(7993), 134-147.

Bavel, J.J.V., Baicker, K., Boggio, P.S., et al. (2020). Using social and behavioural science to support COVID-19 pandemic response. Nature human behaviour, 4(5), 460-471.

Kerr, J., Panagopoulos, C. & Van Der Linden, S. (2021). Political polarization on COVID-19 pandemic response in the United States. Personality and individual differences, 179, 110892.

van Der Linden, S., Roozenbeek, J. & Compton, J. (2020). Inoculating against fake news about COVID-19. Frontiers in psychology, 11, 566790.