The problem with such studies is that they don't demonstrate causation: does college make you successful or do most successful people just go to college?

Right, but it seems more accurate to attribute the income discrepancy to the productivity of those people, rather than "oh you went to uni here's extra money". This means we need to decide if "people who are super-productive tend to go to uni at some point" or "uni produces super-productive people".

different viewpoint on ROI calculations:

The average tuition cost is approximately $16,000 per year. Plus assume another $10,000 in living costs, books, etc. $26,000 in total for a complete cost of $104,000 in a 4 year period. Some people choose to go more expensive by going to a private college and some people choose to go a little cheaper by going public but this is an average. Also, a huge assumption is that its just for a 4 year period. According to the Department of Education, only 54% of undergraduates graduate within 6 years. So for the 46% that don’t graduate, or take 10 years to graduate, this is a horrible investment. But lets assume your children are in the brilliant first half who finish within six years (and hopefully within four). Is it worth it? First, let’s look at it completely from a monetary perspective. Over the course of a lifetime, according to CollegeBoard, a college graduate can be expected to earn $800,000 more than his counterpart that didn’t go to college. $800,000 is a big spread and it could potentially separate the haves from the have-nots. But who has and who doesn’t? If I took that $104,000 and I chose to invest it in a savings account that had interest income of 5% per year I’d end up with an extra $1.4 million dollars over a 50 year period. A full $600,000 more. That $600,000 is a lot of extra money an 18 year old could look forward to in her retirement. I also think the $800,000 quoted above is too high. Right now most motivated kids who have the interest and resources to go to college think it’s the only way to go if they want a good job. If those same kids decided to not go to college my guess is they would quickly close the gap on that $800,000 spread. There are other factors as well. I won’t be spending $104,000 per child when my children, ages 10 and 7, decide to go to college. College costs have historically gone up much faster than inflation. Since 1978, cost of living has gone up three-fold. Medical costs, much to the horror of everyone in Congress, has gone up six-fold. And college education has gone up a whopping tenfold. This is beyond the housing bubble, the stock market bubble, any bubble you can think of. So how can people afford college? Well, how has the US consumer afforded anything? They borrow it, of course. The average student now graduates with a $23,000 debt burden. Up from $13,000 12 years ago. Last year, student borrowings totaled $75 billion, up 25% from the year before. If students go on to graduate degrees such as law degrees they can see their debt burden soar to $200,000 or more. And the easy borrowing convinces colleges that they can raise prices even more. http://www.jamesaltucher.com/2010/02/dont-send-your-kids-to-.... http://www.jamesaltucher.com/2011/01/10-more-reasons-why-par.... http://www.jamesaltucher.com/2011/01/8-alternatives-to-colle....