It’s a complex question that is fairly new to science. Despite high rates of both poverty and mental disorders around the world, researchers only started probing the possible links about 25 years ago.

Since then, evidence has piled up to make the case that, at the very least, there is a connection. People who live in poverty appear to be at higher risk for mental illnesses. They also report lower levels of happiness.

That seems to be true all over the globe. In a 2010 review of 115 studies that spanned 33 countries across the developed and developing worlds, nearly 80 percent of the studies showed that poverty comes with higher rates of mental illness. Among people living in poverty, those studies also found, mental illnesses were more severe, lasted longer and had worse outcomes.

And there’s growing evidence that levels of depression are higher in poorer countries than in wealthier ones. Those kinds of findings challenge a long-held myth of the “poor but happy African sitting under a palm tree,” says Johannes Haushofer, an economist and neurobiologist who studies interactions between poverty and mental health at Princeton University.