HMN 2026: How Meta-analysis challenges the link between economic inequality and mental health

Does living in an unequal society make people unhappy? Not necessarily, reveals the largest study ever conducted on the subject. Nicolas Sommet, a social psychologist and research manager at the LIVES Centre at the University of Lausanne, and his team have published the first social science meta-analysis in the journal Nature. Their conclusions—based on 168 studies covering more than 11 million participants from around the world—challenge the widely held belief that economic inequality is detrimental to well-being and mental health.

A scientific certainty put to the test

For decades, a consensus seemed established in the scientific literature: economic inequality harms the well-being and mental health of populations. Sommet and his international team sought to rigorously verify this certainty—with results that challenge conventional wisdom.

The team reviewed over 10,000 abstracts from ten international databases covering psychology, sociology, economics, epidemiology, and public health. After a rigorous selection process, 168 studies were retained, representing more than 11 million participants across 38,335 geographic units—countries, regions, municipalities—worldwide.

The researchers extracted over 100 variables per article and cross-referenced them with more than 500 World Bank indicators, enabling a contextual analysis of unprecedented depth. The results were then replicated using the Gallup World Poll, which included up to 2 million respondents from over 150 countries between 2005 and 2021.

A statistically null effect

The main finding is clear: the average effect of economic inequality on well-being and mental health is statistically null. More advanced analyses show that this result reflects not only the absence of a statistically detectable difference, but also an effect sufficiently small to be considered equivalent to zero. In other words, living in a society with greater disparities between rich and poor does not, in itself, have a direct impact on individuals’ happiness or psychological balance.

How can we explain that so many previous studies concluded that there was a harmful effect? The researchers identified a significant publication bias: studies with small samples reporting a detrimental effect of inequality on health were overrepresented in the literature, while null results more often remained unpublished.

By correcting for this bias, the research team demonstrated that the estimated effect converges toward zero. Finally, a standardized tool for assessing the quality of existing studies showed that around 80% had methodological weaknesses leading to a high risk of bias.

Inequality as a catalyst rather than a cause

However, further analysis by the research team reveals important nuances. Greater income inequality is associated with lower well-being in contexts or periods of high inflation. Similarly, inequality is associated with poorer mental health in low-income populations.

“Inequality acts as a catalyst that amplifies other determinants of well-being and mental health—such as inflation and poverty—but is not in itself a direct cause of negative effects. This is a much more nuanced view that should be taken into account in public policy,” says Sommet.

Major implications for public policy

These findings have considerable implications. Policies that focus solely on reducing economic inequality are unlikely to have a significant impact on the well-being and mental health of the general population. Instead, the researchers recommend prioritizing the fight against poverty, whose detrimental effects on well-being and mental health are well documented.

The study stands out for its exceptional methodological rigor. The researchers tested more than 1,500 alternative statistical models using specification curve analyses to examine the robustness of their results. They used a machine learning method to identify the main moderating factors, including inflation and poverty, among several hundred candidate variables.

The data and code have been made available to the research community via open access, enabling others to reproduce the results and extend the investigation. This publication is a historic first: never before has this prestigious journal published a meta-analysis in the social sciences—”a huge mark of recognition” for the researcher and his team.

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