Thursday, September 13, 2012

Dutch elections 2012 - poll results

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

Actually, I think the pollsters did pretty well this time. The only thing all of them mispredicted, was a large number of PVV voters moving to VVD, and a lot of SP voters moving to the PvdA, This movement was visible in the last polls leading up to the elections, but the pollsters either underestimated it, or a lot of people switched for the winner on election date.

So, I predicted Synovate would do best, but that did not turn out to be the case. Well, they share first place with Maurice de Hond, but are not clearly better than others. There are lots of blogs, articles and news items about Internet Panels these days. I spent some blogposts on that issue in 2009 myself. Although the largest reason why pollers generally do so badly is that they do not draw random samples, I think there are two more reasons why pollsters do badly. I plan to spend my next two blog posts on these topics, so stay tuned for more on the following issue.

Pollsters use statistical weighting to account for the unrepresentativity of their panel. They do this on sociodemographic characteristics and past voting behavior. I believe it is wrong to weight (in general), and specifically to do so on past voting behavior. I'll show you why in the next days.

No. of seats in partliament 2012
 Maurice de Hond (peil.nl)
Intomart/de stemming
 Synovate
 TNS-NIPO
Exit Poll (synovate)
Final results
VVD (right-liberal)
36
35
37
35
41
41
PVDA (social democrat)
36
34
36
34
40
38
SP (socialist)
20
22
21
21
15
15
PVV (anti-immigrant)
18
17
17
17
13
15
CDA (christian democrats)
12
12
13
12
13
13
D'66 (center liberals)
11
11
10
13
12
12
CU (christian union)
5
 7
5
6
4
5
SGP (reformed christians)
3
3
2
2
3
3
Groenlinks (green)
4
4
4
 4
4
4
PVDD (animal rights
3
2
3
 2
2
2
50plus (elderly)
2
3
 2
 4
3
2







Wrongly predicted
18
24
18
24
6