The percentage of Americans who identify themselves as Christians has dropped by 15% in the past 15 years, a new Pew survey shows. Over the same period of time, the percentage of “nones”—Americans who identify themselves with no religion—jumped by 13%.

Christians remain a majority of the country’s population, at 63%. But the trend suggests that the percentage will continued to decline.

The Catholic proportion of the American population has held more or less steady, slipping only from 24% to 21%.