You may have been surprised at the outcome of the recent British elections, but New Zealand’s experience shows you should not have been surprised that you were surprised …
In about one in three elections under FR/FPP outcomes were markedly eccentric (space has meant leaving out some of the nuances) where parliamentary outcomes did not reflect voters’ wishes (even ignoring the Non-Vote Party). The effect was especially strong when there was a significant third party support reflecting that the populace’s opinions could no longer be treated as simply being on a left-right spectrum.
The surprise then is not that New Zealand switched to an alternative voting system but that it took so long to do so.
The May 2015 British election underscores the same lesson. Labour’s share of votes rose 1.5 percentage points, more than the Conservative’s 0.8 percent;, but it lost 26 seats while the Conservatives gained 24. At the specific level one can explain this by the complexity of the other third of voters switching between a multitude of minor parties. Conservatives got 36.9 percent of the vote, Labour 30.4 percent.*
As I watched the run-up to the election I wondered how anyone could predict the election outcome with confidence. I was not surprised the outcome was surprising.
Brian is right that FPP elections are difficult to forecast in terms of outcomes. However apart from the uneven seat allocations, the polls did still get it wrong by saying Labour and Conservatives were neck and neck when in fact the Conservatives got 6.5% more.