What percentage of landlords only own 1 or 2 properties?

[Michael Wentzel]

My memory has failed me, so I'm looking to the collective memory of BP. 

I think I heard on one of the podcasts that most landlords in the United States only own 1 or 2 properties. In my mind it came out of @Brandon Turner's mouth. The point was most landlords don't run their real estate investing like a business and often burn out. I would love to use the statistic in my business plan that I am using to pitch investors and banks. Unfortunately, I've been searching the internet for statistics and haven't come up with anything.

Does anyone else remember this? Do you have a source to back it up? Or did I make it up?

Mike