The bar chart discribe the quality of families in the US by their annual income in 2007,2011 and 2015, and there were five different kinds of earnin level.
Overall, in the different three periods ,the number of families in the US which earn $75,000-$99,999 a year was the smallest. The households in the US which earned $50,000–$74,999 a year always ranked fourth. The quality of the US families earned $100,000 or more always made for the largest numbers.
In the three different years, the number of families earned $100,000 or more ramined at more than 25 millions , but in 2015, the figure was more than 30 millions. The households can earn $25,000-$49,999 usually ranked at more than 25 millions in the three years. In 2007, there were 25 millions households earned less than $25,000, but in 2011 and 2015, the number of these families increased to more than 25 millions.
The quality of families in the US earned $50,000-$74,999 a year didn’t have obvious change, it was always remained at more than 20 millions in the three periods. The households in the US which earned $75,000-$99,999 a year remained as the smallest number, in 2007 and 2011, the quality made for less than 15 millions, and in 2015, it was increased to 15 millions.