What is happiness inequality? It's the psychological parallel to income inequality: how much individuals in a society differ in their self-reported happiness levels. Since 2012, the World Happiness Report has championed the idea that happiness is a better measure of human welfare than standard indicators like wealth, education, health, or good government. And if that's the case, it has implications for our conversations about equality, privilege, and fairness in the world. We know that income inequality can be detrimental to happiness: According to a 2011 study, for example, the American population as a whole was less happy over the past several decades in years with greater inequality. The authors of a companion study to the World Happiness Report ... found that countries with greater inequality of well-being also tend to have lower average well-being, even after controlling for factors like GDP per capita, life expectancy, and individuals' reports of social support and freedom to make decisions. In other words, the more happiness equality a country has, the happier it tends to be as a whole. On an individual level, the same link exists; in fact, individuals' happiness levels were more closely tied to the level of happiness equality in their country than to its income equality. Happiness equality was also a stronger predictor of social trust than income equality - and social trust, a belief in the integrity of other people and institutions, is crucial to personal and societal well-being.