Evidence gaps

• More evidence needed on the relationship between wealth levels and propensity to make (and size of) political contributions - e.g. At what level of wealth do individuals become major political donors?
• Emerging evidence links wealth inequality democratic backsliding, further studies could estimate the predicted risk of democratic erosion for different levels of wealth share held by the top 10%, 1%, 0.1%
• More, non-US-centric evidence - e.g. Inequalities in political and campaigns donations is found in many countries, but most studies of the impacts of money in politics are US-centric
• More research needed on the effect of wealth inequality on corruption (as distinct from income and as distinct from effect of corruption on wealth)

Social cohesion

• Evidence on wealth and wealth concentration, as distinct from income inequality, remains extremely limited across both social trust and crime outcomes. In particular, despite indications that measures more sensitive to upper-tail income concentration often predict stronger effects (in relation to both social trust and crime) , more evidence is needed in relation to extreme wealth
• Most studies assume linear relationships; there is limited evidence on thresholds, tipping points, and non-linear effects
• More research is needed on the mechanisms linking extreme wealth to lower trust, including status anxiety, perceptions of unfairness, social fractionalisation, and elite segregation, including on whether extreme wealth has effects that differ qualitatively from broader inequality

Social mobility

• A precise threshold at which extreme wealth becomes socially harmful for social mobility is not found
• Evidence is strongest on sticky ceilings and the persistence of advantage among the wealthy, rather than on how extreme wealth affects the mobility prospects of less-wealthy groups
• More research is needed on how contextual factors and institutional regimes moderate wealth-mobility relationships across countries - e.g. how they steepen wealth gradients at the top and reinforce rank persistence,
• Limited evidence on the role of wealth (rather than income) inequality in generating opportunity hoarding and mobility barriers
• Evidence remains concentrated in the US and a small number of European countries, with limited evidence from developing economies

Economic growth

• Limited identification of thresholds and non linearities, particularly for wealth inequality (limited to specific countries or subsample of low-income countries)
• Broader and more systematic distinction between sources of wealth (inherited, politically connected, market-generated) and between types of capital (e.g., luxury vs productive) across different contexts
• Improved top tail wealth data including offshore assets
• Assess heterogeneity in the growth effects of wealth inequality across development levels, financial development, and institutional contexts - for example, between productive institutions and those that facilitate rent-seeking and elite capture
• Country-specific studies and or regional/sub national analyses

Poverty

• More evidence is needed directly examining the link between wealth inequality and poverty - most of the evidence concerns income inequality. This can include an examination of net effects and an assessment of the overall balance of these effects and the institutional conditions under which wealth concentration is more or less compatible with poverty reduction
• There is a clear lack of research around wealth concentration and extreme wealth in relation to inclusive growth and the triangle inequality-growth-poverty
• More research on the impact of policy capture and poverty is needed. Current evidence focuses on unequal responsiveness rather than on how policy capture by wealthy actors bears on poverty outcomes or its impact on poverty reduction
• Beyond income poverty, more research on the impact of extreme wealth and wealth concentration on a range of forms of disadvantage could explore links with housing deprivation, material deprivation, debt stress, insecurity, or broader multidimensional poverty indicators
• More cross-country comparative research can strengthen the assessment of mechanisms and examine how institutional factors (welfare regimes, housing systems, labour-market institutions, tax systems) mediate the relationship between extreme wealth concentration and poverty outcomes

• Evidence remains skewed towards studies focused on income rather than wealth. More econometric studies are needed to examine the impact of wealth concentration and extreme wealth on emissions
• A stronger connection is needed between emissions inequality and the environmental impacts of inequality. While a growing literature documents the disproportionate emissions of top income and wealth groups, stronger evidence is needed on how this concentration translates into aggregate environmental harms, or the identification of extreme wealth thresholds
• More empirical evidence is needed around political economy channels (elite influence, lobbying, structural power) and their connections with other mechanisms and harms. In particular, political economy mechanisms have rarely been studied through the lens of quantifying the impacts of extreme wealth and the relationship between political and environmental harms
• The present focus is on emissions and climate change, but a more comprehensive assessment could examine the role of extreme wealth in relation to different environmental harms (e.g. biodiversity and land-use; resource depletion and pollution) and distinguish/identify common mechanisms