But before I begin, a caveat: Don't use this data to try to figure out how much you or your student is going to pay at any particular college. Don't tell me the averages are too low. This is NCES Data, and it's not always exactly what it's made out to be. For instance, it seems that the growth in for-profit institutions has skewed the private costs low; I'd prefer to show only four-year, not-for-profit private universities, but that data does not go back quite as far, and I thought the longer trend was more interesting. For reference, using just not-for-profits in 2012 would bump the average shown from $35,074 to $39,302. Adjust accordingly.
Still, there is some interesting stuff, not the least of which is the trends from 1969 to about 1981 for private institutions. Up until then, tuition increases largely followed inflation. Note the rapid split after that date; the same thing happens at public institutions about ten years later.
Also, notice that the rate of increase at publics has increased in recent years, having caught up to privates and surpassed them (of course, a larger increase on a smaller base is still, in this case, a smaller number.)
What else do you see?