In the US, this subject appears to have been of quite a bit of interest, and keeps popping up in the media every once in a while. Here's WSJ's Mary Pilon with the latest:
Most researchers agree that college graduates, even in rough economies, generally fare better than individuals with only high-school diplomas. But just how much better is where the math gets fuzzy.
These estimates about the average advantage that says nothing much about the earnings distribution. With that caveat in mind, let's look at the figures: they range from a high of about $800,000 (in a 2002 Census Bureau report) to a low of just about $300,000 (from a 2009 report by Mark Schneider, a vice president of the American Institutes for Research).