According to the graph, it shows as the GPA increases so do the yearly income per person. Also, my mom has told me that it was a lot easier to get a job in a factory because of there were more jobs around. Jobs then left and the economy. Now everybody is competing for a job. The best way to get that job over someone is to have a good GPA and a further education than just high school. My mom who didn't even graduate high school was able to make a living but if I were to drop out research shows it would be almost impossible to make a living.
Better grades were linked to the amount of money someone earns per year. According to the graph, the higher the GPA the higher the salary. It has to do with grades because grades determine your GPA. The higher the GPA the better your grades were, the lower the GPA the worse your grades were.
The type of people who earn the most money is males. I got this off the graph. To be particular it's not just males, it's white educated males. Why that is, I don't have a really good answer. This subject is just hard to give an answer. What I mean by that is we're talking the United States job force. There is approximately 131.1 million jobs total in the US, which many are different. http://money.usnews.com/money/careers/articles/2011/09/28/15-stunning-statistics-about-the-jobs-market
My best answer is we're still a male dominated society. I don't mean any disrespect to women, but statistics are statistics. We have made progress from the past but men still make more money. Also about the race part of it, is most businesses are owned by white men who hire other white men. The equality of the US job force will never be settled. We have been trying for over the last 50 years. It's a thing that you as an individual can't control and also it's hard for the government. It's kind of like the stock market, it will take care of itself. The best advice is get a further education, because it increases your chances.