According to the U.S. Census Bureau, in 2013 the population median income was estimated to be $29,127 for white females, $26,006 for black females, $41,086 for white males, and $30,394 for black males. Compare the difference in median incomes between males and females for

(a) white subjects,

(b) black subjects. If these are close estimates of the population medians, explain why there is interaction and describe its nature.