Having a rat around for the world's highest to lowest proportion of property investors (by country), not able to source some general info yet, but found this, quite interesting, is 2004 keep in mind:
http://www.rba.gov.au/publicationsandresearch/bulletin/bu_may04/bu_0504_2.pdf
Reserve Bank of Australia Bulletin:May 2004
Residential Property Investors In Australia.
http://www.rba.gov.au/publicationsandresearch/bulletin/bu_may04/bu_0504_2.pdf
Reserve Bank of Australia Bulletin:May 2004
Residential Property Investors In Australia.