King's College London

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Allowing wealthier countries, communities, or individuals to opt out of collective solutions to global challenges such as climate change can increase inequality and leave vulnerable populations exposed, according to a major international study co-authored by Dr Sanchayan Banerjee of King’s College London.

Published in the Proceedings of the National Academy of Sciences, the study, led by the University of Nottingham, was conducted by 72 economists and psychologists, drawing on data from 7,500 participants across 34 countries. It identifies a “private solution trap” in which the availability of individual, self-protective measures undermines collective action.

Global collective action problems such as addressing climate change and tackling pandemics require international co-operation if they are to be solved. But in an unequal world, wealthy individuals and nations can opt out of collaborative ‘public’ solutions and fund their own private solutions – such as building flood defences and excessively stockpiling vaccines.

These private solutions form a trap because, according to the study, they can divert resources away from more efficient shared solutions, exacerbate existing inequalities, and leave more vulnerable individuals and communities unprotected.

In order to understand more fully the choices people make between public and private solutions, the researchers created a game in which groups of four students – two “rich” and two “poor” – were given high or low budgets that they could invest in a public solution (benefiting all group members) or a private solution (benefiting only themselves) across ten rounds. Achieving either solution meant they avoided losing their remaining budget.

The study finds:

• Only 15 of the 1,151 groups opted wholly for the public solution; while just 11 opted wholly for private solutions. The majority of groups were split between the two options.
• Across all 34 participating countries, the “rich” consistently invested more in private solutions than the “poor”: 62 per cent of rich players adopted the private solution compared to 32 per cent of poor players.
• Poor players contributed a greater proportion of their funds towards the public solution than their rich counterparts – 40 per cent compared to 31 per cent.
• As a result of these patterns of behaviour, wealth inequality had increased in every country by the end of the game.
• The odds of poor players losing everything were estimated to be more than five times higher than they were for rich players.
• Players in countries which value harmony above hierarchy were more likely to invest in the public solution.

Dr Sanchayan Banerjee, Senior Lecturer (Associate Professor) in Economics and Public Policy at the School for Government, King's College London said:

“We find that inequality doesn’t just shape outcomes—it actively undermines collective action. When private solutions are available, wealthier individuals opt out, creating a ‘private solution trap’ that weakens public systems and deepens inequality”