Matthew Yglesias points us to a nice table showing household(*) income over the past few decades. I've graphed the data, going from 2004 back to 1980, below:

The red and green lines correspond to median income (red in current dollars, green in 2004 dollars); the blue and orange lines are mean income (blue in current dollars, orange in 2004 dollars). Recall that the mean involves adding up all the income and dividing by the number of households; the median is the amount for which we can say that half the households are above this income level and half below. I think it's almost always useful to see a graphical representation of tabular data, even if there are a few pitfalls to avoid in interpretation.

We can see a few obvious things here: Income has been rising relatively steadily over the past 25 years, by all measures. We know that income is skewed toward the upper end (i.e., households that are very rich are not balanced out by the same number of very poor households), which means that mean income is greater (50% greater in 2004) than median income.

The graph shows a few things that might be harder to figure out from looking at the table of numbers. We notice that the green line (marking the inflation-adjusted median income) is moving upward only very slightly over time. Looking back at the actual numbers, we find a 15% increase between 1980 and 2004--that's an average increase of just over half of one percent (0.6%) per year. Another striking pattern in this graph is that the red and blue lines are not parallel, and the blue line gets steeper as we move to the present. In other words, mean income is not only more than median income, but it's increasing at a faster rate. The same pattern is present (though a bit harder to see) for the inflation-adjusted numbers. There are different possible explanations for this, but clearly the rising economic tide is not lifting all boats equally.

Let's finally consider the happy talk from the Bush administration about how well the economy has been doing under his watch. They might tell people, "Look! You're earning more than you did in 2000, when Bush was first elected. Isn't that great?" Unfortunately, if you adjust the numbers by inflation, you see that both mean and median incomes are down, and have been moving downward every year that Bush has been in office.

(*: Apikoros, a commenter on TPM, noted an error in the original description of this data: it's household income, not per capita income as I'd originally written.)