Now, here are many of the problems with all of the income studies that have been brought forward.
Volatility in income:
http://www.debatepolitics.com/econom...post1058996184 (Following Income: Some Problems)
Immigration (which can lower income in a group even if everyone is improving):
http://www.debatepolitics.com/econom...post1058998855 (Following Income: Some Problems)
Retirement and household income (which also implies problems because of # of people working at home, divorces, etc.):
http://www.debatepolitics.com/econom...post1058998862 (Following Income: Some Problems)
And how about a video about how the middle class income is rising.
reason.tv - Videos > Living Large (watch the whole video, it becomes more academic past the anecdotal beginning)
And this is a whole book about income study problems:
Amazon.com: Income and Wealth (Greenwood Guides to Business and Economics) (9780313336881): Alan Reynolds: Books: Reviews, Prices & more