SALT LAKE CITY, May 22 (UPI) -- Mormon millennials are leaving the church at about double the rate of their parents and grandparents, according to a new book that draws on a study of four generations of current and former members of The Church of Jesus Christ of Latter-day Saints.

"We used to keep about three-quarters of people who grew up Mormon and now it's less than half," said Jana Riess, author of The Next Mormons: How Millennials Are Changing the LDS Church.

For LDS millennials -- the generation born from 1980 to 1998 -- the retention rate is 46 percent, Riess said. The problem is not unique to Mormonism, she said, noting that other faiths also are experiencing a drop in their membership.

The book is based on a 2016 survey of 1,156 Mormons and 540 former Mormons in the United States by Riess and Benjamin Knoll, a politics professor at Centre College in Danville, Ky., who helped analyze the data. Riess, a senior columnist for Religion News Service who lives in Cincinnati, also conducted dozens of in-depth interviews.

They describe the survey as the most extensive collection of Mormon attitudes, beliefs, and behaviors collected by independent or academic researchers to date.

Reasons to leave

Eight out of 10 millennial Mormons are white, making them a little more racially diverse than LDS members 52 or older, who are 93 percent white. Older Mormons skew heavily Republican, while the millennials in the church are 46 percent GOP, 41 percent Democrat and 13 percent Independent, according to the survey.

Ninety percent believe in God.

The study shows that LDS millennials are not as progressive as their non-Mormon millennial peers but not as conservative as their parents and grandparents, Riess said.

No one factor has driven the departure of members, she said. Feeling judged or misunderstood and not trusting the church leadership to tell the truth surrounding controversial or historical issues tied in the survey for the top reason cited for leaving the LDS Church by the millennials. (The historical issues themselves weren't motivators to leave -- the fact that they didn't hear about them from their ecclesiastical leaders was).

"Millennials are most troubled by Joseph Smith practicing polygamy but least troubled by consenting adults who might wish to practice polygamy," Riess said.

The millennials' top two reasons also figured into the decision by members of older generations to leave but didn't rank as high, Riess said.

"Stopped believing there was one true church" was the most common reason for leaving given by Gen X members, with the Boomers and the Silent Generation citing not being able to reconcile personal values with those of the church.

Third for millennials who left was the church's position on LGBT issues, which didn't even make the top 10 on the list of reasons given by Silent Generation and Boomer Mormons who left the church. Of the current millennial Mormons, more than half say homosexuality should be accepted by society.

Other reasons for leaving included not being able to reconcile personal values with those of the church, drifting away from Mormonism, no longer believing there was one true church, the emphasis on conformity and the role of women in the church.

"Millennials have a different relationship to authority than previous generations," Riess said. "The majority expressed more reservations about unconditional obedience. They were more troubled by women not having the priesthood."

Alcohol, coffee

For Knoll, the study's most surprising findings were how many Latter-day Saints, including active members of the church, admitted to occasionally drinking alcohol or coffee.

The Word of Wisdom, the church's health code, tells members to abstain from alcohol, coffee, tea, tobacco and illegal or recreational drugs. Of current millennial and Gen X members (those in the generation preceding millennials) who responded to the survey, 40 percent said they had consumed coffee in the past six months, and in a separate question, fewer than one-third of them said avoiding coffee and tea was an "essential" part of a Mormon identity.

The most significant take-away was that while younger Mormons are disaffiliating at higher rates than in the past, the survey indicates "most millennials, as well as all members in general, are faithful, active and generally very happy with their participation in the LDS Church," Knoll told UPI in an email.

Noting that younger members are more diverse in both their religious belief and practice than previous generations, he added, "A key question going forward will be the extent to which LDS Church leadership and the broader community will be willing to welcome and integrate a more diverse generation of members going forward."

Riess and Knoll plan to use the study data to write a book on former Mormons and what their lives were like after leaving the LDS Church.

More information on the study is available online.

The Salt Lake City-based church, which was founded in 1830 in New York state, has about 16.3 million members worldwide.