Christmas music: Do you hear what I hear? Again and again and again?

From Nate Silver’s website comes this interesting look at the music we keep hearing during this time of year: 

Radio’s wall-to-wall holiday format is a recent development. Of course, stations in the past played some Christmas music on Dec. 24 and 25, but the vast majority of soft-rock stations began switching to all-holiday soundtracks in the 1990s. The first to throw out its regular playlist entirely was 99.9 KEZ (KESZ-FM) in Phoenix, in 1991 or 1992.¹ The variety station saw a substantial jump in its ratings, and the trend eventually caught on nationwide.

Radio programmers, as well as music-streaming services such as Spotify, do a healthy amount of planning, data work and market research to create seasonal soundtracks that people want to hear — but not hear too soon. Streaming services need to keep subscribers happy, and doing so requires sophisticated algorithms to keep Christmas out for 11 months and cranked up for one. For radio, the stakes are even higher. A station that flips its format can see its ratings triple in an especially good December (and gain from the commensurate advertising that comes along with them).

But when is the best time to push the holiday tunes?

Darren Davis, iHeartMedia’s president of networks² and a former programmer in several major cities, laid down what’s going through the heads of people behind the playlist at your local radio station.

“Some programmers decide far in advance exactly when they’re going to start,” Davis said. In areas where there’s competition in the Christmas sector — “that holiday battle” among stations, Davis called it — programmers can be ready to flip the format at a moment’s notice in an effort to keep up with or beat the competition. In the past, Davis said he never picked a specific date, but instead was prepared to make the switch by Nov. 1 — just in case.

“That could be a sudden cold snap coming in, and it starts snowing one afternoon. It could be some big thing going on in the world where everybody’s in a bad mood, and they need a little pick-me-up,” he said.

This year’s flips are mostly behind us, so we can see when they happened. At least 184 iHeartMedia stations in the U.S. and Canada are airing holiday music; there was a huge jump right after Thanksgiving.

The demand for holiday music started to pick up even earlier. Glenn McDonald, who’s in charge of developing the genre algorithm at The Echo Nest, a research company owned by Spotify, provided FiveThirtyEight with the combined number of daily plays of two iconic Christmas tunes — “All I Want For Christmas Is You” by Mariah Carey and “White Christmas” by Bing Crosby — to serve as a sort of Spotify Christmas Industrial Average. Looking at the demand for those two songs from Nov. 1 to Dec. 8, we can see a substantial jump in streams Dec. 1.

So what are the songs you keep hearing? Check out the link for the definitive list, with all the supporting data.