But other scholars see an array of possible reasons, including the view that more women than men join the Utah-based Church of Jesus Christ of Latter-day Saints.
The report, "Mormons in the United States 1990-2008: Socio-Demographic Trends and Regional Differences," released Wednesday by Trinity College in Hartford, Conn., found that 60 percent of Utah Mormons are women, up from 52.5 percent two decades ago.
It also showed that the state's Mormon majority continues to shrink, down to 57 percent, although Utah remains the only state where a religious denomination accounts for more than half the populace.
The report relies on data culled from the American Religious Identification Survey, which is built on a large, nationally representative sample of 113,723 respondents in 1990, including 1,742 self-identified Mormons, and 54,461 people with 783 Mormons in 2008. Children were not counted in the survey.
The national LDS response for the 2008 poll has a margin of error of 4 percentage points, according to the authors. The Utah survey of 270 Mormons 161 females and 109 males has a margin of error of about 5 percentage points.
Like most Christian denominations in the United States, Mormonism "has a surplus of women," Phillips and Cragun write. "In 1990, this surplus was more pronounced among Mormons outside Utah, where 54.9 percent of Latter-day Saints were female, compared to 52.5 percent in Utah. By 2008, a dramatic shift had occurred. While the male-to-female ratio actually narrowed somewhat in most of the nation, it widened significantly in Utah. Females now outnumber males in Utah 3 to 2."
In the past, Mormon men remained tied to the church rather than lose their social standing in the community, argue Phillips and Cragun, both on the board of the Mormon Social Science Association. "However, declining Mormon majorities [in Utah] may have weakened that link, and Mormon men who lack a strong subjective religious commitment to the church are now free to apostatize without incurring sanctions in other social settings."
They further speculate that women who cannot find LDS marriage partners often wed outside the faith, becoming more vulnerable to divorce. In addition, children born to "mixed-faith marriages are less likely to remain in the church."
David Campbell, a political scientist at the University of Notre Dame and co-author of American Grace: How Religion Divides and Unites Us, questions the authors' conclusion about men leaving the LDS fold in greater numbers.
The discrepancy could be, Campbell said, that either "more women are coming in or more men going out. Or it could be both of these things and there may be other hypotheses, too."
Marie Cornwall, editor of the Journal for the Scientific Study of Religion, also challenges the report's conclusions about women.
"They are not taking into consideration any conversion or in-migration," said Cornwall, a sociologist at LDS Church-owned Brigham Young University who wrote an essay on women in Contemporary Mormonism: Social Science Perspectives. "They have no way of knowing whether the growing gap reflects migration patterns professional men and women leave the state to look for jobs and, given the lower rates of professional women, that may mean that men are leaving the state as much as it means that they are leaving the [LDS] Church."
The LDS Church had no specific comment on the survey's data, spokesman Scott Trotter said Wednesday. "We have seen surveys such as this before. Some seem to overestimate and some underestimate various elements of [LDS] Church-related statistics. Ultimately, we reach out to individuals, not numbers."
By all indicators, including the faith's global building program, Trotter said, "the church is growing, and we are grateful that people are embracing the gospel of Jesus Christ."
In 2008, 91 percent of U.S. Mormons identified themselves as white, 3 percent as black, 3 percent as Latino, and 3 percent as other. Utah is even more homogeneous, with 95 percent of that state's LDS population describing themselves as white.
Mormonism is slowly getting more diverse nationally, with Latinos accounting for most of the change. LDS missions have been established in Africa, as well as in Latin American nations.
The data show that Mormons are generally better educated than non-Mormons. College graduates comprise 29 percent of all Mormons and 31 percent of Mormon adults in Utah.
Mormons in Utah had significantly larger households in 2008 than Mormons elsewhere 4.2 people per household versus 3.7 people per household, respectively suggesting that the traditional norm of large families endures in Utah.
The period of 1990 to 2008 saw rising prosperity, with above-average increases in household income among Mormons in Utah. In both the 1990 and 2008 American Religious Identification Survey, Mormon households in Utah seem to have increased their incomes relative to non-Mormon households.
Source: "Mormons in the United States 1990-2008: Socio-Demographic Trends and Regional Differences"