Start here:
http://www.pewforum.org/2011/12/19/g...denominations/
and here:
http://www.pewforum.org/2006/10/05/p...resource-page/
For a more specific target, that is, the AoG, see here:
http://www.charismanews.com/world/50...-growth-trends
and for Oneness, see here:
https://www.amazon.com/Our-God-One-T.../dp/1888251204
Roughly half a billion Pentecostals and Charismatics in the world today, and Talmadge French estimated that of that number, only about 30M were Oneness.
This worldwide growth of Pentecostals and Charismatics has been happening for the last century or so. Having this many people claim a Pentecostal or Charismatic identity, which, as a movement or subgroup of Christianity proper, is chiefly recognized for its belief that when one receives the Holy Spirit, they speak in tongues, indicates that some very large number self-identify this way because they have themselves spoken in tongues as they received the Holy Spirit.
Now, if we subtract French's estimates from the total number, we still have about 500,000,000 people in the world today claiming a Pentecostal or Charismatic heritage.
But, if even less than half of these 500M have actually received the Holy Spirit and spoken in tongues, that's still over 200M more than those in the Oneness camp.
If even only 1/5 have done so, that' still way over the number of Oneness who have, by about 70M.
If merely a tithe have done so, that's still 20M more.
I suppose, if one were so inclined, one could conclude that all the research done by French and the Pew Forum folks is faulty beyond hope, and therefore, these numbers can be rejected out of hand.
And as far as the impossibility of proving one thing or the other, if you're looking for some ace in the hole to prove your point, then more power to you. Play your card.
But before you do, remember the creator of this thread admitted she received the Holy Spirit in a Trinitarian church. Didn't you say the same about yourself? My memory is a little foggy (I think you addressed it in one of Originalist's threads about Jimmy Swaggart a few months back. Not sure, though).
And speaking of Originalist, he was a licensed member of the AoG, and received the Holy Spirit there. I'm sure he can assure you that the people in the AoG, to pick a group, are by and large receiving the genuine article.
Maybe navygoat can chime in here, if even comes around anymore.
My cousin received the Holy Spirit in an AoG church. So did my mother in law, and my wife, when she was five, and going with her mom to an AoG Sunday school. They've all converted to Oneness since then, and none of them have needed to exchange what they had already received.
Are there charlatans and fakers out there? Of course, in every movement, even among Oneness. Remember Borat, or the so-called Cracker Barrel revival video with the old guy getting in on the prayer action, spazzing out and doing stuff either in his flesh or worse?
Here it is in case you haven't seen it before (skip to the 2:00 minute mark):