I so often I hear people making the general statement that the poor are getting poorer while the rich are getting richer. While there is a kernel truth to this statement it needs to be examined and dissected to really understand it.
Professor Steven Horwitz, PhD of economics at St. Lawrence University can do a much better job at explaining this than I.
This video is a brief explanation on income mobility. For a more in depth explanation of this topic I have also posted a lecture by Professor Horwitz.
Inequality, Consumption, & Happiness.