The night after the election, one can conclude that all pollsters in the Netherlands did a bad job of predicting the election results. All polls were at least off by 20 seats (out of 150), and I expect the newspapers to make headlines of this in the next days. See the table below for the final predictions (before election day), the exit poll and final election results. The last row shows how much each poll was off (in the number of seats
Many opinion pollers do badly when it comes to predicting elections. This is mainly because they let their respondents self-select them into their polls. So what, who cares? The polls make for some good entertainment and easily fill the talk-shows on television. If everyone knows they cannot be trusted, why care?
We should care. In the Dutch electoral system - with poportional respresentation - every vote counts. If only a small percentage of voters lets their vote depend on the polls of the election result, this can result in shifts of several seats in parliament.
There are several ways to do an exit poll, but they all come down to asking people what they voted, right after they went into the voting booth. The first succesfull modern exit poll was conducted in 1967 to predict the governor’s election of Kentucky .
One of the difficulties in exit polling, is that some people might not want to say whom they vote for, especially if this person is politically controversial.
Opinion pollers do a lousy job of predicting elections. For a good read, see for example the prediction of the New Hampshere primary in 2008, when all polls predicted Obama to win, but it was Clinton who won (albeit by a slim margin).
In the Dutch context, there are three main polling firms, that each do equally well (or badly). Out of a hundred and fifty parliamentary seats, peil.nl mispredicted 20, while TNS-NIPO and Synovate shared the honor of only missing the target by 16 seats in the 2010 parliamentary election.