Owners of 40 per cent of homes in capital cities purchased over the last two years are in a "negative equity" position, analysis published yesterday by research firm RP Data shows.Across Australia that proportion is 33 per cent.RP Data bases its estimates primarily on trends in property prices (using the firm's own housing price analysis) rather than on complementary data on loan-to-valuation ratios across the financial system.The firm estimated that 6.4 per cent of all households were in a position of negative equity at the end of December 2011, up from 4.9 per cent at the end of September.RP Data estimates that property prices across all capital cities fell by 3.8 per cent over the course of 2011. The firm put price declines over the first two months of 2012 at 0.2 per cent.