The commercial statistics were compiled from information in caveats lodged at the option stage with the Singapore Land Registry. 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 1998-Q4 are used as the base reference price of the index (i.e. the index for 1998-Q4 assumes a value of 100).The indices are compiled based on a Moving Average weight method, whereby the value of properties transacted in the past 12 quarters are used as weights.