Many reasons have been proffered for the huge swing towards the People's Action Party (PAP) in the 2015 General Election ("Fear for Singapore propelled vote swing"; last Sunday).

But there seems to be one reason not mentioned at all.

This is the first time since independence that all the seats were contested.

Some of those not contested in previous general elections were PAP strongholds, and the opposition parties found them not worth contesting. Incidentally, these are the constituencies that garnered some of the highest vote shares in GE2015, notably Tanjong Pagar GRC, which used to be helmed by the late former prime minister Lee Kuan Yew.

Mathematically, these constituencies' high percentage votes have pulled up the overall GE2015 percentage. Based on my calculations, if Tanjong Pagar GRC had been contested in 2011, the PAP would have garnered more than 63 per cent of the vote share, instead of the 60.1 per cent that it actually received that year.

So, perhaps, the swing in GE2015 would have been 7 percentage points, instead of the close to 10-percentage point swing in the results. As a matter of accuracy and for it to be meaningful, the calculation of the swing has to assume roughly the same cohort of people voting.

Assuming that all constituencies will be contested at the next general election, we can then make a more meaningful comparison of the swing in vote shares (be it for the PAP or the opposition) with the results of GE2015.

Matthew Yeo Cheng Heng