The dramatic rise in inequality has corresponded quite neatly with the decline in union membership, according to an analysis from the left-leaning Economic Policy Institute.

As EPI notes, that divergence in income growth, especially noticeable since 1979, corresponds with a decline in union influence, as an increase in union membership would help to boost worker incomes. Indeed, if the incomes of the union rank-and-file rose by just one-tenth, middle-class incomes would go up $1,479 per year, even for middle-class families who aren’t union members, according to a September analysis from the Center for American Progress.