5 meaningful contacts with Christians before considering the claims of the gospel

I've been reading a book on Church growth (*Growing A Healthy Church* by Dan Spader and Gary Mayes) with a chapter on evangelism that says something which I've heard in churches before: >"Typically a**n unbeliever needs to have more than five meaningful contacts** with a number of Christians before he or she will begin to trust the message of the gospel Growing a Healthy Church This seems to be a linchpin point supporting relationship-style evangelism but the book doesn't cite any sources and I don't seem to be able to find any myself. **Can someone else locate the source of this claim whether it be a study or merely an idea proposed by someone else?**