What's your basis for 10-20% being raptured? It would be wonderful if that percentage of the population were Believers... That percentage may be church goers, but how many of those are actually Christians?
Statistics and polls are always coming up with the figure that 40% of Americans are Christians and Church-goers. In my book "Sifted Generation" I did a lot of research on this topic. That 40% figure is completely wrong. - I believe it is around the 10-15% range. I was being liberal with 20%
The Truth about Church Attendance
A recent study I found extremely fascinating, yet, sadly disturbing is titled, 7 Startling Facts: An Up Close Look at Church Attendance in America, by Rebecca Barnes and Lindy Lowry. Through their methodologies they have documented what I, and many evangelicals, have known for years; that the popular polls on church attendance are not reporting accurate results. Under the subheading, “Less than 20% of Americans regularly attend church — half of what the pollsters report”, they state: While Gallup polls and other statisticians have turned in the same percentage— about 40% of the population— of average weekend church attendees for the past 70 years, a different sort of research paints quite a disparate picture of how many Americans attend a local church on any given Sunday. Initially prompted to discover how church plants in America were really doing, Olson, director of church planting for the Evangelical Covenant Church (covchurch.org), began collecting data in the late “80s, gradually expanding his research to encompass overall attendance trends in the Church. In his study, he tracked the annual attendance of more than 200,000 individual Orthodox Christian churches (the accepted U.S. church universe is 330,000). To determine attendance at the remaining 100,000-plus Orthodox Christian churches, he used statistical models, which included multiplying a church’s membership number by the denomination’s membership-to-attendance ratio.
His findings reveal that the actual rate of church attendance from head counts is less than half of the 40% the pollsters report. Numbers from actual counts of people in Orthodox Christian churches (Catholic, mainline and evangelical) show that in 2004, 17.7% of the population attended a Christian church on any given weekend. 2 (bold print is mine). Shocking?? It shouldn’t be. If those were the facts in 2004 than I do not think I would be wrong in stating it has declined even more since then. I have seen similar results in my own unprofessional tracking time and again. Below is one such chart that illustrates the standard polling data often gathered. This chart is courtesy of the Pew Research Group.
See Chart here https://content.gallup.com/origin/gallupinc/GallupSpaces/Production/Cms/PMCMS/c7qcrr6afkmocddvjgauhq.png
Barnes and Lowry go on to report on a phenomenon that is very much in line with biblical teaching on the sinful inclinations of humanity (see Rom. 3: 23; Eccl. 7: 20; 1 John 1: 8). What they reveal is that people generally want others to think of them as being good, to do this they will often lie to others about their activities. To make their point they show that the work of sociologists C. Kirk Hadaway and Penny Long Marler, who are known for their scholarly research on the church, wholeheartedly agree with Olson’s findings:
What Hadaway and Marler, along with Mark Chaves, author of the “National Congregations Study,” discovered was at play is what researchers call “the halo effect” —
the difference between what people tell pollsters and what people actually do. Americans tend to over-report socially desirable behavior like voting and attending church and under-report socially undesirable behavior like drinking. 3 (emphasis added)
So if the studies are correct, and I believe they are, we can conclude with little doubt the lack of emphasis on sharing Christ with the nonbeliever and the huge dips in church attendance are more than likely linked. In America, sharing the gospel and encouraging growth in Christ is just not happening at the level it once was.
Michael L. Henderson. The Sifted Generation: Tested, Tried, and Found True (Kindle Locations 1060-1078). WestBow Press. Kindle Edition. 
