Pop country followup

I looked at coarse patterns in subject of country and pop music, but these folks did a much more thorough study of "reproductive messages" in pop, country, and R&B for 2009. Figure 3 (page 11) is a longitudinal review; there's an interesting shift in the content of R&B. They even go back into classical music as well to see if the same patterns persist. (Found as a link from this article which says that popularity is partly driven by peer pressure. Not a huge surprise, of course...)