This Coleman Insights study, "What Happens When Music Gets Played?" (download 28-page PDF) came out last year but I didn't see it until recently. It looks at what happens when a new country song is played, what the differences are for male/female artists and new/established artists, and how long it takes for that song to peak (about 450 spins on average).

Among the findings: Country radio audience grows 1.8% two minutes into exposure to a new song, established artists perform better than new artists, uptempo songs perform better than slow songs, and male artists perform better than do female artists (the difference lessens for new artists).