I doubt those numbers are very low. Having grown up in the bible belt, I've seen many "cultural Christians" who make me think those numbers are really, really high.
78.4% of our nation CALL themselves Christian. But how many of those have put money, celebrity, politics, family, lust, or self before God in their lives? How many actually make it to church on Sunday morning (or any other time), or pray? How many are actually travelling down the narrow path that Jesus speaks of?
It's one thing to call ourselves Christian. It's another to actually BE one.