With the exception of outside data sources, all-music radio stations have use the same process since Top 40 radio was created in 1952 in the aftermath of the AFM's loss of the ability to control recorded music on the radio.
The station programmer and staff hear new songs. They decide which ones they'd like to play, based in part on what they are already playing. They wait for feedback, and move the song up, down or out.
In the 50's and 60's, we tracked juke box play and singles sales. By the late 50's we had the first of the tip sheets, The Gavin Report, which showed us what stations across the country were playing. So if we saw a song that we did not add making progress in other markets, we would take another listen.
By the mid to late 70's, some of us had callout to get listener feedback on the songs we were playing and that made up for the elimination of singles sales as a guide.
Now we also can see nearly instantly the movement of downloads and on-demand listening to help us play the songs listeners like.
Stations programming pop music have essentially been using the same techniques for 65 years... just the methodology has changed.