Ever turn on the radio and think wow, all these songs sound the same? Especially in the summer?

A new opinion piece in the New York Times claims there’s a reason for that — with scientific data to back it up. Just look to Spotify. The music streaming service has a mathematic algorithm that analyzes songs for placement in customized playlists. It computes statistics on tracks based on five factors:

Loudness… average volume of a song

Energy… how fast and noisy at song sounds

Danceability… strength and regularity of the beat

Valence… how cheerful a song sounds

Acousticness… the likelihood that a song uses acoustic (or “real”) instruments

When analyzed, an image (or “sonic fingerprint”) is created for each song. The Times used hits by Gloria Estefan, Richard Marx and Def Leppard as examples of “songs of the summer” candidates from 1988. When analyzed, the three songs contained disparate combinations of the above factors. In other words, they all sound dramatically different from one another.

By the time, 2010 rolled around, pop songs were starting to sound the same. When analyzed through Spotify’s algorithm, hits by Katy Perry, Kesha and Lady Gaga has sonic fingerprints that are almost interchangeable.

The Times says over time, there’s been less variety in the top-10. Fewer rock bands are having hits these days, for example. Pop stars are also relying on the same songwriters and producers, which further homogenizes the product. Max Martin. for example, has written more than 20 number-one singles for the likes of Katy Perry, Justin Timberlake and Katy Perry.

“The hit-making process has become less random than it once was,” says Larry Miller, director of the music business program at the Steinhardt School at N.Y.U.

The period form 1987 to 1990 shows far more variety among hit songs than the period from 2009 to 2012. However, the Times claims there is hope on the horizon, citing recent hits by Post Malone, Cardi B and Drake as a new era for innovative hip-hop and R&B.

“Things are loosening up a little,” says David Penn, founder of Hit Songs Deconstructed, a company that analyzes pop music. “The old Katy Perry sound doesn’t fly anymore.”