[keebEz]

With the 1980 chart: if we should be ensuring high income growth to people according to their income percentile alone then gradually you'd assume they'd move up along the curve (since its income, and not wealth, and income*growth over time would move to the right then).

In this world, everyone would slowly move up the curve according to their tenure/age.

However, if we believe that people should have income growth more dependent on their willingness to work (rather than just income percentile) then over time, with high income growth on the low end, those most willing to work would move up.

In this world, then the income growth is a dependent variable of 'willingness to work' and logically would move up the income percentile over time as labor re-sorts itself into higher income growth percentiles based on that willingness to work.

One simple chart doesn't tell you much. It'd be best to see cohort effects across this time period to see if the bottom percentile is a bunch of 18 year old kids now (millennials), versus a bunch of prime age baby boomers itching to work hard.

Having said that, the cohort effects I've seen are reassuring, but there are still big issues. The main point is that this chart isn't that great at saying anything conclusive.