Psychologist E. Glenn Schellenberg and sociologist Christian von Scheve teamed up to comb through five decades of Billboard Top 40 hits. They find that, over time, our taste in pop music has veered toward more and more depressing songs:

Analyzing Top 40 hits from the mid-1960s through the first decade of the 2000s, they find an increasing percentage of pop songs are written using minor modes, which most listeners—including children—associate with gloom and despair. In what may or may not be a coincidence, they also found the percentage of female artists at the top of the charts rose steadily through the 1990s before retreating a bit in the 2000s.

Strikingly, they found “the proportion of minor songs doubled over five decades.” In the second half of the 1960s, 85 percent of songs that made it to the top of the pop charts were written in a major mode. By the second half of the 2000s, that figure was down to 43.5 percent.

Classical music actually went through a similar development, moving more toward minor songs between 1600 and 1900. The changes in pop music modes, the researchers note, have come much faster, over the course of decades rather than centuries.