Investors with multiple residential investment properties have "contributed to higher risk" for banks and other lenders, an analysis by the Reserve Bank of Tax Office data has found.Drawing on ATO data covering 13 million individual tax returns (up to 2015) to provide insights into households' property investments, the RBA summary highlights the evolving risks being absorbed by lenders.There is "evidence that changes over time may be increasing risks," the RBA wrote in its half yearly Financial Stability Review.The RBA listed three core themes; "the rise in the share of households with multiple investment properties and in the share of investors over the age of 60 with mortgage debt, as well as investment across state borders where the investors' knowledge of the property market can be lower."In 2014/15, the RBA said, "11 per cent of the adult population, or just over 2 million people, had one or more investment properties. The share of these with mortgage debt has remained around 80 per cent since 2008."In recent years the share of negatively geared investors has declined in line with interest rates, the RBA said, though this "remains over 60 per cent of total investors. With many not earning positive income from their property, prospective capital gains are more likely the primary rationale for investing."Leveraged property investment draws affluent first timers back for more.Around 70 per cent of investors own just one property, the RBA said.However, around half of investment properties are owned by investors with multiple properties; 20 per cent of investors own two properties and ten per cent own three or more. "The number of investors with multiple properties has grown relative to those with a single property, particularly between 2013/14 and 2014/15," the RBA said."Indeed, the number of investors with five properties grew by 7.5 per cent in that one year, compared with average growth of 4.5 per cent over the previous nine years."