Fuzzy Math

In 2012, the mean annual income of the bottom quintile of American households was $11,490. In 1979, the comparable figure (adjusted for inflation) was $11,808. Seeing that $11,808 is bigger than $11,490, I am at a loss to explain how Bret Stephens thinks that the mean annual incomes of the bottom quintile of American households have increased by 186% since 1979.