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seat 2pp graphs '07

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  Mumble poll-mix

 

Summary

Go to recent poll-mixes

This fortnightly poll-mixing differs from Reuters and other poll averages in several ways. 

It is not done every fortnight, but more regularly than that

On each calculation, it finds the most recent poll and looks at all polls over the fortnight up to then

It weights for time passed, so a poll conducted today counts twice as much as one held two weeks ago. But "time-weight" only applies to most recent fortnight, not past ones

It weights for sample size

I'm getting, from two major pollsters, numbers to one decimal place rather than to the nearest integer

I estimate two party preferreds from the pollsters' data. Ie I don't use the pollsters' 2pps

 

- Go to recent poll-mixes 

Read on only if you wish to get more technical ...

Crunching the polls

First, a word of warning. I am not a statistician, and some of my crunching might appear, to practitioners of that trade, a little unsound. I welcome suggestions for improvement - but in reasonably plain English please.

Reuters poll trend

You might be aware of the Reuters Poll Trend, which comes out once a month. It uses something called the “ Henderson moving average” to crunch together three regular polls. You can read more about it here.  

(The ABC's 'Insiders' program also runs a weekly trend graph, but I can't find any reference to it online.)

The Reuters graph is a fine thing, but it has some shortcomings. For one thing, it doesn't include Galaxy. Reuters have their logistical reasons for this, but Galaxy's excellent record since materialising out of nowhere in 2004 makes them a must-include.

Nor does Reuters include any of the irregular, small polls that appear from time to time.

They also use pollsters' published numbers that are rounded to the nearest integer (except Morgan, which goes to the nearest .5), do their Henderson magic and then publish the result to 0.1 percent. This seems unsound to me.

I reckon we can do better. From now until election-day I’ll be regularly mixing up the polls, using my own herbs and spices, and publishing headline two party preferred numbers to the nearest half a percent.

My coup

The biggest coup is that two pollsters have very kindly agreed to provide to me, from now until the election, their voting intention data to one decimal place. I won’t be publishing those numbers, but they will greatly improve the quality of my aggregates. (One of those helpful pollsters is Galaxy; the other prefers to remain anonymous but is also one of the Big Four.) 

I'm not using the pollsters' two party preferred numbers, but am estimating from their primary numbers. Three of the four main pollsters arrive at 2pp like this anyway, although using different strategies.
 
Test-driving my formula on the final published polls before the 2004 election gives 52.5 to 47.5 in the Coalition’s favour - very close to the actual result of 52.8 to 47.2.  

I'm weighting for sample size, which allows me to include wonky little surveys that appear from time to time. 

I'm also weighting for time that has passed since the poll was taken, which is admittedly iffy and subject to revision. That is, on any given day I look at all polls taken in the last fortnight, and the further back the poll was taken the less it counts. 

More detail

Notionally distributing preferences by minor party is tricky, because different pollsters give different minor party data. Everyone publishes a number for the Greens, but not necessarily for Democrats, Family First and One Nation. Yet whether these parties are extracted also affects the makeup of the "others" number.

I allocate .75 percent of Greens to Labor. This is actually less than the .81 which flowed in 2004, but I reckon with Bob Brown not as close to Kevin Rudd as he was to Mark Latham, .81 is too high. The 2001 number was about .75. 

For the preference flows from other minor parties and the rest, I used (roughly) the numbers from this APH paper.

Those who are that way inclined can see my Foxpro/DBase formula here; field names are self-explanatory. (But like sausages and the law, it's not something I particularly recommend.)