Civil conflict has plagued much of Africa, with ethnically diverse countries experiencing particularly high rates of violence. Yet within these nations, patterns vary, leading to questions of why some groups rebel while others do not and why a given group rebels at certain times but not at other times.

In a paper in the American Economic Review, author Eleonora Guarnieri untangles the factors that drive groups to rebel against their central government. She shows that when ethnicities become more culturally distant from those in power, their likelihood of engaging in civil conflict increases significantly.

Her research suggests that conflicts arise as a result of ethnic favoritism in resource distribution and from fundamental disagreements over the types of public goods that central governments should provide.

Guarnieri recently spoke with Tyler Smith about how she estimated the impact of cultural distance on civil conflict, and what her findings may mean for reducing violence across Africa's diverse societies.

The Clean Air Act has been an essential tool for reducing air pollution in the United States. But standard estimation methods may overstate its impact, according to a paper in the American Economic Journal: Economic Policy.

Authors Lutz Sager and Gregor Singer reexamined the 2005 regulations targeting fine particulate matter (PM2.5) and found that improvements in air quality were closer to a 3 percent reduction in pollutants rather than the 10 percent suggested by conventional methods. However, they also found that the benefits from cleaner air may be larger than previous estimates suggested.

Sager and Singer recently spoke with Tyler Smith about methods for properly estimating regulatory impacts that feature time trends and the implications for other measures based on estimates of air quality improvements.

The patchwork nature of America's public safety net has evolved over centuries, shaped by political winds and changing views on poverty. Understanding this complicated history may help shed light on the core tensions that continue to define debates about who deserves assistance and how it should be provided.

In a paper in the Journal of Economic Perspectives, author Christopher Howard explored how programs targeted at people with low incomes expanded from meager, local support in colonial times to the large-scale programs of today. He draws a distinction between two parallel systems: means-tested programs targeted specifically at low-income Americans and inclusive social insurance programs available to citizens across income levels.

Howard recently spoke with Tyler Smith about the surprising political durability of some targeted programs, the dramatic success of Social Security in reducing elderly poverty, and the ongoing gaps in the public safety net that leave many Americans vulnerable.