Until yesterday I had never heard about the hidden job market, I am genuinely interested.

Re this bit

The Australian Bureua of Statistics publish the stats on the number of people starting work in a given period. The recruitment industry know how many jobs were advertised via them/job boards (I do not personally have access to that information). That's the equation - See more at: http://www.pomsinadelaide.com/forum/...tml#post294102
Where do people who move from one job to another come into this?