Which came first -- the cig or the poverty?

A new analysis of federal smoking data shows that "Smoking, the leading cause of preventable death in the country, is now increasingly a habit of the poor and the working class . . .This growing gap in smoking rates between rich and poor is helping drive rising inequality in health outcomes . . ."

So which came first? Are these people more likely to smoke (an expensive habit) because they are poor, or are they poor because they waste money on expensive cigarettes?

"Smokers crowd lower income levels." The Dallas Morning News; March 25, 2014; p. 7A.