Researchers Kathleen Napier and Lior Shamir from Lawrence Technological University in Michigan have published a research paper in the Journal of Popular Music Studies, showing how the lyrics from 6150 songs from the Billboard Hot 100 list have changed over the years. The team used quantitative analytics to study how the lyrics have changed. A text-mining program called Tone Analyzer, part of the computational linguistic tools in IBM Watson Developer Cloud. This service uses linguistic analysis to detect joy, fear, sadness, anger, analytical, confident and tentative tones found in text. There's a demo of Tone Analyzer that you can use to analyze text to see how it works, along with an API reference showing how to use Tone Analyzer in your own projects.

 

Tone Analyzer was used to apply automatic quantitative sentiment analysis, which associates all the words and phrases in a piece of text - in this case the song lyric - with a set of tones that they express. The individual tones are then combined to provide an overall sentiment. In the study, the sentiment measures for all the songs in the Billboard Hot 100 songs for a year were averaged, giving an annual score. This was then used to work out how levels for that sentiment - anger and sadness - changed over the decades.

The analysis showed that the hits released in the mid 1950s had the lowest levels of anger, though the three years from 1982-84 were equally low in angry lyrics. Generally, though, the lyrics became more angry and sadder over the analysis period.Levels of disgust and fear also grew over the years, though not as markedly as anger and sadness. Songs became more angry particularly in the mid 1990s, with levels peaking in 2015, according to the study. An equally depressing finding was that joy as a sentiment dropped steadily from the 1950s to present day, apart from a brief period in the mid 1970s.