Beginning 2017 what estimate of individuals own bitcoin? How many different individuals in the world own bitcoin?

I.e. John owns .5btc, Michelle 300btc, Al 4000btc : the answer would be 3.

I am interested in the percent of the global population that owns bitcoin as it would be a good indicator of the potential (and value) further for bitcoin as it is educated to more and more people and eventually reaches mainstream (hopefully).
There's a hard limit on the amount of people that own one bitcoin: There currently are only 16.1 million bitcoins in circulation, so there can't be more more than 16.1 million people with one bitcoin. However, there are a number of individuals that control much more bitcoin than that, so it is safe to say that the actual number of users that own one bitcoin is much smaller, I'd guess less than one million people.

On the other hand, the number of users that own any bitcoin at all is very hard to estimate as well. There are currently 46 million unspent transaction outputs, so if we'd assume that every user maintains their own balance that would be a strict upper limit. However, many users leave their coins to be managed by online wallets or exchanges, so it's not a reliable limit. On the other hand, the number of people is probably even much smaller than that, because few people own many of those UTXOs. If I were to hazard a guess, I'd say that there are fewer than five million people in the world that own any bitcoins.