A study on coal mining in Appalachia suggests that ""the presence of coal in the Appalachian region has played a significant part in its slow pace of economic development. Our best estimates indicate that an increase of 0.5 units in the ratio of coal revenues to personal income in a county is associated with a 0.7 percentage point decrease in income growth rates. No doubt, coal mining provides opportunities for relatively high-wage employment in the region, but its effect on prosperity appears to be negative in the longer run.""