Some interesting figures I'm going to rehash from a site I read:
There are about 6 billion people in the world. About half are female. Five out of seven are of an age where they are likely to masturbate. Kinsey says 60% of women masturbate. Surveys indicate that, of the women who do masturbate, they average one or more times a week and an average masturbatory session lasts about 4 minutes.*
So, in any average 4 minute period,
6 x 10^9 x 0.5 x 5/7 x 0.60 x 1/(7x24x60) (per minute) x 4
Equals ... roughly half a million (500,000).
So, at any one time, about 500,000 women are masturbating at the same time with you!
This also means that, when you orgasm from masturbation, you are doing it in synchrony (during the same second) with about 20,000 women ...
Which means, if you are male, that there's a lot of lonely women out there, and, if you're female, that you are not alone ... not by a long shot.
* - One big assumption is that the population of the world is distributed evenly (which it isn't). The biggest assumptions would be in the frequency of masturbation and the average length of one session. However, the assumptions don't sound like they would be too far off reality anyway - and if so, not by more than an order of magnitude or two, which still means you are never alone ...
I guess a similar calculation could be done for males, but the surveys (Cosmopolitan, Kinsey, The Hite Report, etc.) have been more thorough on females...