The goal of the graph is to generalize large scale income distributions/gains on a large sample size of hundreds of millions of people. Not to go into every si

The goal of the graph is to generalize large scale income distributions/gains on a large sample size of hundreds of millions of people. Not to go into every single micro sub group of income earners and divorced neurologists with company sponsored health insurance who have more income than an tech worker homeowner with 6 cats. The graph is perfectly valid for what it represents. The share on a large sample size of hundreds of millions of people of historical income gains and results can be interpreted thusly.