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Maybe you've noticed,live sex video but researchers have discovered pop songs in the last 30 years have become sadder, but more danceable at the same time.

The paper, published in Royal Society Open Science, analysed music trends and success over 500,000 songs that made the UK top 100 charts between 1985 to 2015.

Researchers from the University of California Irvine found that over the last few decades, there's been a "clear downward trend" in bright and happy songs, and a slight upward trend in sadder songs. The "maleness" of songs, has also decreased.

When it comes to successful songs (which researchers measure as being in the top 10 or staying in the charts for a long time), they tend to be "‘happier," more "party-like," less "relaxed" and more "female" than most.

"The public seem to prefer happier songs, even though more and more unhappy songs are being released each year," the report notes.

Recently chart-topping songs noted as being on the sadder side of the index included Sam Smith's hit "Stay With Me" and "Unmissable" by Gorgon City, which compares to the prevalence of popular happier songs from the '80s like "Would I Lie to You?" by the Eurythmics, and "Freedom" by Wham!

The researchers used machine learning techniques to predict whether a song would be successful, based on its musical features.

When adding what they dubbed a "superstar" variable, which applied to artists which have had a top hit in the previous five years, the researchers had a 85 percent success rate in identifying a hit.

Perhaps there's a formula to pop music after all.

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