Median incomes are not growing as fast as they should be. This is true. And it is a serious problem.

[Donald Ian Rankin]

35. The median is the income of the middle person.

Suppose I have 21 people, with varying incomes.

Then the median is the income of the 11th-richest.

The incomes of the poorest 10 and the richest 10 don't have any direct effect on the median, even if they go up or down, except that if one of them crosses that middle income then the person who was 11th richest is now 10th or 12th, someone else is now the 11th richest, and so the median is now their income.

In some ways it's a more useful measure than the mean (that is, the sum of all the incomes divided by the number of people) - if I have 20 people earning $20,000 and one earning $20,000,000,000 then the median is $20,000 while the mean is $1,000,000,000, and the median probably gives you a better guess as to what life is like for most people.

But all it tells you about is the middle person - the people poorer than them could be a little poorer or a lot poorer, the people richer than them could be a little richer or a lot richer, but the median will still just be their income.