Popular songs today are more depressing than those from three decades ago

Researchers at the University of California, Irvine, have determined that modern pop music is more depressing than tunes from three decades ago.
Their study determined that music from 2015 is about 20% more unhappy than it was in 1985. Researchers looked at the lyrics and acoustic properties of hundreds of thousands of songs and came to the conclusion that music isn’t has happy as it used to be. (See articles by AP, Paper and the Daily Mail.)
Judging from the current list of hit songs, the trend is continuing. The top 10 songs in the U.S. this week include such downers as “This Is America” by Childish Gambino, “Psycho” by Post Malone, and “No Tears Left To Cry” by Ariana Grande.
Coincidentally, iHeartRadio is publicizing an application called Graduation Playlist that lets you see what songs were popular in the year you graduated from school.
My high school graduation year (1980) included such hits as “Any Way You Want It” by Journey, “Another Brick in the Wall, Pt. 2” by Pink Floyd, “Heartbreaker” by Pat Benatar, “What I Like About You” by The Romantics, “Brass In Pocket” by The Pretenders, “Train in Vain” by The Clash, “He’s So Shy” by The Pointer Sisters, “Upside Down” by Diana Ross, “Refugee” by Tom Petty and the Heartbreakers, “Misunderstanding” by Genesis, “Hungry Heart” by Bruce Springsteen, and “Boulevard” by Jackson Browne.