Fewer Americans believe in God, pray daily and regularly go to church than in 2007, a poll says.

More than 35,000 Americans were polled about their religious beliefs over four months in 2014 by the Pew Research Center. The study, called the 2014 Religious Landscape, was released Tuesday. It updates research done seven years ago.

The Pew Research center said the percentage of Americans who are "absolutely certain" God exists fell to 63 percent from 71 percent.

One reason for this, the center says, is the large population of young adults – called Millennials – who say they don't belong to any religion.

The other reason is that older, more religious Americans, are dying.

The people who don't belong to a religion are called "nones" by the survey's writers.

"Nones" made up 16 percent of the adult population in 2007. This time around, the number is 23 percent.

Among the "nones," about 61 percent said they believed in God.

But the research center said there is a "great deal of stability in the U.S. religious landscape" in spite of the lower numbers.

Within the category of people who are affiliated with a religion, the numbers stayed mostly stable.

Seventy-seven percent of the people surveyed said they were connected to a religion, down from 83 percent in 2007.

In that group, 89 percent of those surveyed said they believe in God, which was only a small change from the last time the survey came out.

Alan Cooperman, the Pew center's director of religious research, says those who identify as "religious" are as observant as ever.

"On some measures, there are even small increases in their levels of religious practice."

The survey asked Americans about a number of hot-button issues related to religion.

The survey looked at Americans' views on homosexuality, abortion and evolution.

People who identified as Christian were about 10 percent more accepting of homosexuality than they were seven years ago. Most Christian institutions officially oppose homosexuality.

Views about abortion were mostly unchanged compared with the survey seven years ago. Fifty-three percent of Americans said abortion should be legal in most cases.

About evolution, 62 percent of Americans said they believed humans evolved over time. Thirty-four percent said they did not believe in that theory.

I'm Kelly Jean Kelly.

This story appeared on VOANews.com. Dan Friedell adapted it for Learning English. Kathleen Struck was the editor.