Here is what Residex say about how they do it all from their site  http://www.residex.com.au

The unique Residex database cannot be matched by any public or private organisation in terms of accessible historical data and completeness.

Residex provides information on all aspects of the real estate market, not just relating to price, but also rental yield, growth in prices, analysis of market movements, mortgage design, financial transaction structuring, raising and placing of funding facilities, loan risk profiles, statistical consulting, price estimation and research.

The company is consultant and adviser to state and federal governments on housing related issues including the development of financial instruments to provide funding for housing needs.