Here's the Statistics on "Modern Finney-ism"

At a 1990 crusade in the United States, 600 “decisions for Christ” were obtained. No doubt, there was much rejoicing. However, ninety days later, follow-up workers could not find even one who was continuing in the faith. That crusade created 600 “backsliders”—or, to be more scriptural, false converts.
In Cleveland, Ohio, an inner-city outreach brought 400 decisions. The rejoicing no doubt tapered off when follow-up workers could not find a single one of the 400 who had supposedly made a decision.
In 1991, organizers of a Salt Lake City concert encouraged follow-up and discovered, “Less than 5 percent of those who respond to an altar call during a public crusade . . . are living a Christian life one year later.” In other words, more than 95 percent proved to be false converts.
In 1985, a four-day crusade obtained 217 decisions. However, according to a member of the organizing committee, 92 percent fell away.
In his book Today’s Evangelism, Ernest C. Reisinger said of one outreach event, “It lasted eight days, and there were sixty-eight supposed conversions.” A month later, not one of the “converts” could be found.
A church in Boulder, Colorado, sent a team to Russia in 1991 and obtained 2,500 decisions. The next year, the team found only thirty continuing in their faith. That is a retention rate of 1.2 percent.
According to Pastor Elmer Murdoch, “Chuck Colson . . . states that for every 100 people making decisions for Christ, only two may return for follow-up a few days later. George Barna says that the majority of people (51 percent minimum) making decisions leave the church in 6–8 weeks.”
Between 1995 and 2005, Assemblies of God churches reported an amazing 5,339,144 decisions for Christ. Their net gain in attendance was 221,790. That means that 5,117,354 (over five million) decisions could not be accounted for.
Charles E. Hackett, the national director of home missions for the Assemblies of God in the United States, said, “A soul at the altar does not generate much excitement in some circles because we realize approximately ninety-five out of every hundred will not become integrated into the church. In fact, most of them will not return for a second visit.”
In Sacramento, California, a combined crusade yielded more than 2,000 commitments. One church followed up on fifty-two of those decisions and could not find one true convert.
In Leeds, England, a visiting American speaker acquired 400 decisions for a local church. Six weeks later, only two were still committed and they eventually fell away.
In November 1970, a number of churches combined for a convention in Fort Worth, Texas, and secured 30,000 decisions. Six months later, the follow-up committee could find only thirty still continuing in their faith.
A mass crusade reported 18,000 decisions—yet, according to Church Growth magazine, 94 percent failed to become incorporated into a local church.
Pastor Dennis Grenell from Auckland, New Zealand, who has traveled to India every year since 1980, reported that he saw 80,000 decision cards stacked in a hut in the city of Rajamundry, the “results” of past evangelistic crusades. But he maintained that one would be fortunate to find even eighty Christians in the entire city.
A leading U.S. denomination reported that during 1995 they secured 384,057 decisions but retained only 22,983 in fellowship. They could not account for 361,074 supposed conversions. That is a 94 percent fall-away rate.
In Omaha, Nebraska, a pastor of a large church said he was involved with a crusade where 1,300 decisions were made, yet not even one “convert” was continuing in the faith.

Source: "God Has a Wonderful Plan for Your Life, by Ray Comfort, 1999