NASHVILLE (AP) — With the 2012 presidential election looming, a Vanderbilt University political scientist says the one key factor is the disposable income of voters.

Larry Bartels says if the real disposable incomes of voters are growing in the six months before Election Day, President Barack Obama is likely to win. Disposable incomes include income from wages, investments, tax cuts and government benefits.

He says more familiar indicators like unemployment and gross domestic product seem to matter much less, probably because they are not as closely tied to the average voter's sense of economic well-being.

Bartels has researched voter trends for more than three decades.