How much does a college droupout cost?

According to a survey of the "Stifterverband für die Deutsche Wissenschaft" Germany loses about 2.2 billion euros a year because of college dropouts. They also claim that if you include private investments and evaded incomes, the loss is as high as 7.6 billions.

How did they calculate this figures? For a scientific society there's quite a lack of sources (in words: zero). They give us a hint that they "correlated" the following datas: rate of college dropouts, average costs of a college place per year and average study time of college dropouts. I don't know how exactly they "correlated" those numbers, but I suspect, that they used a fairly (say: way too) simple calculation model. Using their reasoning it would also be quite a sound claim to say that it's best to shut down all the universities as soon as possible because students are a huge economical loss.

Let's think about it: If the average cost of a certain study place are about 10,000 euro a year and, say, we have ten dropouts. Does somebody (the state or the university) get 100,000 euro paid onto his bank account? I don't think so, because in a lot of courses, it doesn't actually matter whether you're teaching 100 or 150 students because most of the costs are fixed (the only thing that varies are the average costs of the college place depending on the number of students). On the other hand, is it really fair to consider the money spent on a college dropout lost? There are a lot of succesful college dropouts (and if you're using the reasoning from the "Stifterverband" they're actually earlier generating money in the economy than they're still studying counterparts at the university).

But we haven't faced the most important (and what actually should have been the first) question yet: What is a college dropout? Someone who quits college completely or someone who just switches his college courses? (Or some variation of this...). Think of someone who begins studying computer science as major and math as minor and finds out that she's just more a math type and therefore swaps her major and minor. Would you call her a dropout (she might turn up in some statistic as such)? Did she do any economical damage to the state (perhaps there were some slight administrative costs)?

What I want to say is, that some people have (in my opinion) far too simple views on this topic. I myself have actually no idea how you can calculate the cost of a college dropout and I even don't know how to find a good definition of a college dropout, but I think we should sort out this kind of questions first, before we are going to throw are trusty old Humboldtian university ideas over board and begin to restrict access to the universities and lose the academic liberties.