previous poll 6.5% confidence limits 4.28% — 8.88%
this poll 9% confidence limits 6.4% — 12.1%

the confidence limits overlap between the two polls thus no change is seen at the 95% confidence level. This is based on an effective sample size of 400 (down from their 800 but I’ve still been generous given the reductions due to all the differences between a “simple random sample” and what is actually done in the field).

Roy Morgan just offered an explanation for a non significant result. He’s not the only one and I don’t mean to single him out. Most of the changes in polling which are commented on are not significant. Could do better.

David, you said “we dont expect to see the green poll result to go from 3% to 9% because of sampling error”. Perhaps not, but the Roy Morgan comment was based on Greens going from 6.5% to 9% and that’s what I’ve used in my analysis. I just don’t see the point of spending the money on collecting the data and doing the analysis and not bothering to use the correct formulas. But then that’s just me. Bugger the pollsters.

BTW, the percentage cutoff is generally 20% or 80% for using the kind of normal based approximation which accompanies the Roy Morgan report (Zar p379). That means every analysis for smaller parties should be based on a more accurate calculation of confidence limits.

The issues you raise about effective sample size are all important ones, but even if your rule of thumb is roughly accurate, we only see the error bars increasing by a factor of 1/sqrt 2.

So here, we dont expect to see the green poll result to go from 3% to 9% because of sampling error. The smaller party poll results at this time of the election cycle seem to be very volatile and could well relate to specific news events. In some ways, polls at this time are irrelevant because we are not having an election tomorrow so people arent actually thinking about who they will vote for.

They have done their time and Kiwis with an extraordinary sense of fairness want the other team to have a turn at batting.

Anybody who actually thinks like this is stupid.

And young Johnny is going to step up first and hit a maiden century on his debut.

If he gets in I’d say it would be the exact opposite. He’s shown conclusively that he has no leadership capability, doesn’t know his parties policies, doesn’t seem to have even a basic grasp of economics or, more importantly IMO, psychology.

The only things he’s shown that he can do is smile, flip flop and prevaricate. He doesn’t do those very well either.

Bravo to you both for the discussion – very useful!

According to polling theory, the absolute estimates for small parties are more accurate, not less, in a random poll than for large parties.

So the variation we are seeing is not sampling variation – it probably shows greater awareness of a smaller party for some reason. Around election times, the polling numbers for small parties fluctuates less as we see more of them and people are actually thinking about who they might vote for rather than responding to the latest political news.

Burt – do you read what you are saying? You’re saying Labour should do something (what – stand down, snap electon? You haven’t even articulated what they should be doing, yet you attack the ‘apologists’ for its defence!) because they haven’t got support over 50%, and that it is bad to justify Labour not doing whatever it is because National also didn’t do this unarticulated act.

What an odd line to pursue.

P.S didn’t your mate Robert actually have a go at that back in the 80’s? Didn’t work out that well, but then he was pretty drunk.

P.P.S burt – I see a twinkling of Socialism peeking through. I’m not sure you would see it, but I can’t help but think that Liberal Representative Democracy isn’t fulfilling its promise to you. So, my friend, let me introduce you to its cousin, Socialist Participatory Democracy…

AncientGeek then suggests that because the polls are based on landlines they are likely to over-represent some people and under-represent others. This comment is a reasonable one and it would certainly be interesting to test the results of a polls drawn from such a sample against those drawn from a sample that included people without landlines. But to correct AncientGeek (and only in the interests of precision), such a test would evaluate the external validity of the sampling technique not its internal validity. There is absolutely no doubt in my mind that the polls do currently use a random sampling technique and are thus internally valid (if the interpretation of the data is limited to those which the sampling techniques assumptions would support ie a two horse race). The question of how representative the polls are is a separate issue (ie external validity) and one that would be best assessed by a table that compared the sample to the NZ population on key characteristics (age, sex, income, education level etc). With that information at hand and a sample size that is driven by the small party support, one could usefully interpret party support in New Zealand and understand the limitations of the data.

rOb at least has the mental capacity to take the “they did it too” comparison off shore so that he’s not looking like a “Labour good – National bad” muppet. AncientGeek (the brains trust) on the other hand uses the classic Labour defense of “National do it to”.

Keep it up guys, keep supporting the party that thinks it’s OK to break their own laws to combat their slump in the polls.