There are a lot of reasons why would not want to use acces panels for predicting electoral outcomes . These are well discussed in many places on- and offline. I’ll shortly summarize them, before adding some thoughts to why access panels do so badly predicting election outcomes.
1. Access panels don’t draw random samples, but rely on self-selected samples. A slightly better way to get panel respondents is a quota sample, but even these have problems, well discussed here, here and here for example.
**Poll volatility **
Below, you find the summed changes in parliamentary seats over all parties in consecutive opinion polls for the four main polling firms in the Netherlands in the lead up to the 2012 elections. I will update the table below in the next weeks.
This overview follows from my earlier post on Dependent Interviewing. Maurice de Hond (peil.nl) is the only survey pre-loading earlier voter preferences into survey questions.
I was re-reading one of the papers I wrote as part of my dissertation on survey data quality in panel surveys. The paper deals with the effects of the introduction of an interviewing technique called Dependent Interviewing in the British Household Panel Survey. I wrote this paper together with Annette Jackle, and if you are interested after reading the next bit, you can download a working paper version of it here.
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.