Differences between pollsters

David Winter at The Atavism blogs on how different pollsters vary from the average of all the polls, to see which ones have a polling bias. I wouldn’t use the term bias, as that is a loaded word, but it is useful to see the variation. The better comparison will be after the election, against the actual results. However it is still interesting to see this graph:

David’s conclusion is:

It seems TV3 tends to get National a little higher and Labour a little lower than the rest of the pollsters, and perhaps the Herald goes the other way. I think trying to gain anything more meaningful than that from these results is probably the statistical equivalent of reading tea leaves, but feel free to stare at the graph and confirm your own political biases!

As I said, am looking forward to comparing after the election.