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. Nicolas Sommet and his international team sought to rigorously verify this certainty — with results that challenge conventional wisdom.
Research of unprecedented scale
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effect of inequality on health were overrepresented in the literature, while null results more often remained unpublished.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 standardised 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." — Nicolas Sommet, LIVES Centre, University of Lausanne
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 prioritising the fight against poverty, whose detrimental effects on well-being and mental health are well documented.
A historic first for the social sciences
The study stands out for its exceptional methodological rigour. 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 in Nature 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.
Reference: Sommet, N., Fillon, A. A., Rudmann, O., Cunha, A. R. S., & Ehsan, A. (2026). No meta-analytical effect of economic inequality on well-being or mental health. Nature, 626. DOI: 10.1038/s41586-025-09797-z
Open access data and materials: https://osf.io/wstcq/
