Hmm…I haven’t seen such stats and guessing they are hard to find.
Some easy ways to do some guessing is pick a federal agency – in U.S. say Environment Protection Agency which I think has 16,000 employees
If you try to create a Facebook ad, you can target by employer and see how many identify. So say that is 4,000 folks – you can guess 25% is the minimum percentage.
You can do roughly the same thing with LinkedIn