Lyrics are the best predictor of whether a song is a hit.

A new analysis by researchers at North Carolina State University has revealed the most common themes based on lyrics of number one songs on Billboard's Hot 100 chart from the last few decades.

It turns out the most common themes are downers. In the previous decade, the hit song themes were mostly Inspiration, Pain and Desperation. In the 90s it was Loss, Inspiration and Escapism.

The 80s had Loss, Aspiration and Confusion, and the 70s Nostalgia, Rebellion and Jaded. Neuroscience has shown that individuals process lyrics and tunes separately while listening to songs.