Inconsistent data on the types of people taking out home loans has the potential to shake the stability of Australia's financial system, according to the Reserve Bank's Deputy Governor, Philip Lowe.Addressing an audience of financial services professionals ahead of yesterday's Finsia Regulators Panel, Lowe warned that the continuing inability of banks and other home mortgage lenders to differentiate between investors and owner-occupiers is becoming an area of growing concern. He made the point that the importance of high-quality data is far from being an obscure issue."The basis of good analysis is good data. Improvements over time in the quality and comprehensiveness of the data on housing prices have, for example, helped improve the general understanding of housing market developments," he said. Lowe contrasted this with recent changes by banks in how they had recorded and categorised owner-occupier and investor housing loans - this has had the opposite effect, that is, complicating the regulators' understanding of what is going on in the housing market."As lenders have looked more closely, what they have found has surprised and, to some extent, concerned us," Lowe said.He noted that over the past six months there have been very large upward revisions to the value of investor loans outstanding, with offsetting downward revisions to owner-occupier loans. "The cumulative effect of the upward revisions has been to increase the stock of investor credit outstanding by around $50 billion, or ten per cent. According to these new data, investor loans now account for 40 per cent of total housing loans outstanding, not the 35 per cent reported earlier in the year."Some of these earlier errors have been dealt with, but not all. Some lenders are unable to provide comprehensive back data to the RBA, leaving it to "make adjustments" for its investor and owner-occupier credit series.The second "data issue" outlined by Lowe emerged over the past couple of months. It is the reverse situation, where lenders are reporting that loans previously recorded as investor loans should have been recorded as loans to owner-occupiers. This has come about in part from the prudential regulator's actions in forcing lenders to hold more capital against their investors' loans. "When faced with the higher interest rate on investor loans, some borrowers have indicated to their bank that they are not an investor, but rather an owner-occupier, and so should not have to pay the higher rate," Lowe said, warning there is more of the same on the way."Our liaison with lenders suggests that further reclassifications of this nature could be expected over coming months."The various data problems have confirmed the "supervisory focus" on investor lending has been entirely appropriate - along with highlighting that "some lenders' internal systems" have been unable to generate accurate data on the split between investor and owner-occupied housing loans.One consequence of this failure by the home lending sector generally is that APRA, the RBA and the Australian Bureau of Statistics have decided to undertake a thorough review, next year, of the data collected by authorised deposit-taking institutions.