People who say they are unaffiliated with any religion constitute nearly 20 percent of the American public, making them almost as numerous as Catholics, who accounted for 22 percent of participants in a new study.

People who say they are atheist, agnostic or “nothing in particular” grew by almost 5 percentage points since 2007, from 15.3 percent to 19.6 percent of the population.

The greatest shift toward “nothing in particular” apparently came from Protestants, who now make up 48 percent of the population, compared to 53 percent in 2007.