Average income sums up all incomes observed in the country and divides them by the number of people earning those incomes. Because there are often a very small number of very wealthy individuals with very high incomes (e.g. the top 1%), it will distort the average by skewing it upward. A better representation is the median, whereby 50% of incomes appear below the median and 50% above it. This eliminates that upward bias.