I find the articles in this website useful and it also derived the same numbers I crunched a few months back http://propertybuyer.com.sg/articles/

One particularly interesting part mentioned in the articles is there is a misalignment of HDB building programme a few year back. My interpretation is this leads sustained good demand for rental flats this year. Likely once the HDB BTOs & ECs and more condos are ready from 2012 onwards, then it could be much more challenging to get good quality tenants.

The caveat is if more immigrants are allowed to come in after the election, there could be continued good rental demand.