When I was a little boy my grandma, who was illiterate, taught me how to tell if some people are lying. Truth is immutable: persons A and B may live in totally different eras but what they say about a certain truth is the same.
Tharman now (2014) says that the government does indeed use CPF funds for investment.
However in 2007, Dr Ng said the opposite. [see the article referenced by the following link:
http://www.tremeritus.com/2014/07/27/dr-ng-in-2007-gic-did-not-use-cpf-monies/]
The two of them together CANNOT be telling the truth.