In their book Dangerous Intersections, Jay Dennis and Jim Henry write:

Prayer changes things. That’s what a church in Phoenix discovered after the pastor asked members to randomly choose 80 people from the telephone book. He then requested daily prayer for each person for 90 days. At the same time, he asked members to choose another 80 names from the directory, but the second list was simply laid aside and nobody prayed for those people. After 90 days, members called all 160 people on the lists, asking them whether they would allow Christians to visit them to pray for them.

“The amazing result,” says Alvin VanderGriend of the American Lighthouse movement, “was this: only one person on the list of people who did not receive prayer was prepared to allow Christians to visit, whereas 69 of the 80 people for whom the church members prayed were prepared to allow Christians to visit, and 45 even invited them into their houses, offered coffee and named special prayer requests.”