Dorn, D., Fischer, J. A., Kirchgässner, G., &Sousa-Poza, A. (2007). Is it culture or democracy? The impact of democracy and culture on happiness. Social Indicators Research, 82(3), 505-526.

We analyze the relation between democracy and perceived subjective well-being while controlling for other relevant determinants such as culture measured by languages. We conduct a cross-national analysis covering 28 countries using data from the 1998 International Social Survey Programme. Contrasting existing empirical evidence, we observe a significant positive relationship between democracy and happiness even when controlling for income and culture measured by language and religion. The effect of democracy on happiness is stronger in countries with an established democratic tradition.

https://doi.org/10.1007/s11205-006-9048-4