The residential statistics were compiled from information in caveats lodged at the option stage with the Singapore Land Registry, supplemented with Stamp Duty data from the Inland Revenue Authority of Singapore, as well as data provided by developers for new sales. A caveat is normally lodged by a purchaser to protect his/her interest of a property shortly after the option to purchase is exercised. The prices in 2009-Q1 are used as the base reference price of the index. The indices are compiled based on a Stratified Hedonic Regression method. The value of properties transacted in the past 5 quarters are used as weights. The weights are revised every 3 years. The latest revision was in 2015-Q1.