Culture argument can be argued effectively as follows:
If a cohort in Japan has a median score of X at median household income Y, the American cohort with same median score X has income closer to 1.25Y or 1.5Y.
Whether you want to define your American cohort based on geography or ethnicity doesn't really matter-the result will be preserved up to a point.
If a cohort in Japan has a median score of X at median household income Y, the American cohort with same median score X has income closer to 1.25Y or 1.5Y.
Whether you want to define your American cohort based on geography or ethnicity doesn't really matter-the result will be preserved up to a point.