The rental indices for commercial properties (i.e. office and retail space) are compiled from tenancy agreement data from the Inland Revenue Authority of Singapore (IRAS).
To compute the rental indices, rental transactions are grouped by property type, locality etc. The median rental in each group is used to compute a sub-index. The rental index of a particular property type is the weighted average of all the sub-indices of that property type in the various groups. The indices are computed based on a Moving Average weight method, whereby the value of properties transacted in the past 12 quarters are used as weights.