How scientists say a hit song is like an infectious disease

Researchers at McMaster University have found several similarities between the outbreak of an infectious disease and the release of a new hit song. 

The researchers found epidemic modelling can be used to determine what drives the popularity of hit songs, often described as contagious, infectious, or viral.

"When a disease breaks into a population you tend to see a sharp increase in infection cases and eventually it will peak at some point when it sort of makes its way through the susceptible population and starts to decline," Dora Rosati, lead author of the study, told CBC Hamilton.

"We see that same pattern with song downloads in our data. There'd be the sharp increase as more and more people heard about the song and wanted to listen to it, then it would peak and decline."

Rosati said if you think about a song as being "infectious," the analogy continues from there. 

"When you do that you infect other people and then eventually you move on to the next song or you get a little bit tired of this one and you stop listening to it so actively and then we consider you to be recovered, to use the disease terminology," Rosati said.

New songs spread rapidly through a population

According to the researchers, when an infectious disease first enters a population, it is transmitted from person to person through social interactions. The pathogen eventually reaches a peak and then declines as fewer people are susceptible or infectious individuals recover.

After a new hit song is released, it also "spreads" rapidly through a population, from person to person through various media, eventually reaching peak popularity before it loses appeal, the researchers said.

"The most important finding of the study is that we have shown that it makes sense to use a mathematical model of disease spread to study song popularity and that opens the door for all kinds of things that we might be able to learn about song popularity," Rosati said.

"For example right now we can use those models to learns things about an epidemic like how long the epidemic will last, how many people might be infected,what the biggest number of people who are simultaneously infected might be and if we can apply that in a song context we could learn analogous things like how many people in total might download a song, how long the song will be popular for and what the peak popularity that song would be.

"Another significance of the study is that it tells us something about how both music and an infectious disease depend on our social connections to spread through populations," Rosati added.

Researchers obtained data from a database containing 1.4 billion individual song downloads, from 33 different countries, through Nokia cell phones over a seven-year period, which included genres such as dance, metal, pop, reggae, country and western and electronica, a style of music derived from techno and rave. They focused their analysis on song downloads that occurred in Great Britain.

Rosati conducted the research under the supervision of David Earn, a professor in the Department of Mathematics and Statistics, and collaborated with colleagues Ben Bolker, professor in the Departments of Mathematics and Statistics and Biology, and Matthew Woolhouse, an associate professor in the School of the Arts.

They determined the contagious processes that a mathematical model reveals for infectious diseases might also be at work in driving song popularity.  That is, both music and infectious disease depend on social connections to spread through populations.

"Whether it is a disease infecting many people or a song becoming popular, some kind of social contact is required," Earn said. 

"For an infectious disease, this is generally physical contact or breathing the air near an infected person. For a song, the contact might involve physical proximity, but it might also be virtual contact through social media. In either case, transmission relies on social networks."

For example, the modelling suggests fans of electronica share songs more actively or more effectively than other genres such as pop.  The social network of electronica fans might be more strongly connected than other fan communities or they may be more passionate about their favourite songs and bands. 

A whole new way of researching song popularity

According to Rosati, the other significant implication of the results is they open up a whole new way of researching song popularity in the future.

"In the same way that we can now use mathematical models of disease spread to learn things like the average time an individual is infected, the final size of an epidemic, or how long an epidemic will last, we might be able to use these same models to learn things like how long, on average, an individual will listen to a song, how many people in total will download a song, or how long a song might be popular for," Rosati said.

The researchers reported their findings in the journal Proceedings of the Royal Society A.

Woolhouse said the study is a demonstration of the creative and interdisciplinary research taking place at McMaster, adding that it brings together "big data, musical expertise, and mathematical insights." 

Even though the study is not related to the COVID-19 pandemic, Woolhouse said, "given our recent collective experiences, it is sure to capture the popular imagination."