First, the study says, churches appear to be overprotective. Nearly one-fourth of the 18- to 29-year-olds interviewed said "Christians demonize everything outside of the church" most of the time. Twenty-two percent also said the church ignores real-world problems and 18 percent said that their church was too concerned about the negative impact of movies, music and video games.

Many young adults also feel that their experience of Christianity was shallow. One-third of survey participants felt that "church is boring." Twenty percent of those who attended as a teenager said that God appeared to be missing from their experience of church.

The study also found many young adults do not like the way churches appear to be against science. Over one-third of young adults said that "Christians are too confident they know all the answers" and one-fourth of them said that "Christianity is anti-science."

Some also feel that churches are too simple or too judgmental when it comes to issues of sexuality. Seventeen percent of young Christians say they've "made mistakes and feel judged in church because of them." Two out of five young adult Catholics said that the church's teachings on birth control and sex are "out of date."

The fifth reason the study gives for such an exodus from churches is many young adults struggle with the exclusivity of Christianity. Twenty-nine percent of young Christians said "churches are afraid of the beliefs of other faiths" and feel they have to choose between their friends and their faith.

The last reason the study gives for young people leaving the church is they feel it is "unfriendly to those who doubt." Over one-third of young adults said they feel like they can't ask life's most pressing questions in church and 23 percent said they had "significant intellectual doubts" about their faith.

David Kinnaman, Barna Group president and author of the book on these findings, You Lost Me: Why Young Christians are Leaving Church and Rethinking Church, said part of the problem may be that many churches are geared toward "traditional" young adults.

"But most young adults no longer follow the typical path of leaving home, getting and education, finding a job, getting married and having kids – all before the age of 30," he said. "These life events are being delayed, reordered, and sometimes pushed completely off the radar among today's young adults."

The Barna Update that highlights this study also says that today's young adults are heavily influenced by the major social, spiritual and technological changes that have occurred in the last quarter century.

Dan Smith, pastor of Momentum Christian Church in Cleveland, Ohio, told The Christian Post in an email that the six points "resonate" with him.

"I feel like part of God's calling on my life is to reach those 85 percent (made-up stat) who want to connect with God ... but don't feel like the typical church is helping with that," he said.

"Most of our church is made up of 20s, 30s, and 40s – younger people – because our leaders have the same mindset as some of the younger people do – we won't tolerate inauthenicity 'on stage,' trite answers, anti-scientific discussion, etc. As Scripture says, we believe that if Jesus is lifted up, young people should also be drawn to him ... so we try to lift him up in a way they can participate."

Instead of overreacting to these statistics (by gearing churches specifically toward young people) or remaining indifferent to them, Kinnaman suggests that churches should cultivate "intergenerational relationships" within their congregations.

"In many churches, this means changing the metaphor from simply passing the baton to the next generation to a more functional, biblical picture of a body – that is, the entire community of faith, across the entire lifespan, working together to fulfill God's purposes."