My, What a Big Swing You Have.
Posted by Possum Comitatus on September 30, 2007
This time we are going to use the marginal/safe government/safe ALP seat breakdowns in conjunction with the State based breakdowns to not only give us a list of seats and the margins they would be on should the quarterly Newspoll be right, but also some idea of the marginal/safe government/safe ALP vote in each State
So to start with, we’ll draw up a basic table consisting of all the data we need.
|NSW||Vic||Qld||SA||WA||Total seats||Newspoll Swing|
What this shows is the number of marginal, safe Coalition and safe ALP seats in each state, the recorded Newspoll swings in those seat types (on the right) and the overall state swing recorded by Newspoll on the bottom. The 8.8% swing in the bottom right hand corner is the overall national Newspoll swing.
Note here, that I’m only using 139 seats – the seats in these 5 states (that Newspoll use for their breakdowns), however I have taken the 2 independents (Windsor and Katter) out of the mix.
Next up we need to make an assumption. We need to assume that the proportion of the national swing compared to the marginal and safe seat swings is uniform across Australia. Hence, nationally the ratio of the marginal seat swing to the national swing is 8.3/8.8 = 0.94, therefore we will make the assumption that the ratio of the marginal seat swing in NSW divided by the NSW State swing is likewise 0.94.Using this, we estimate that the marginal seat swing in NSW is 0.94 multiplied by the NSW state swing of 9.2, giving us a NSW marginal seat swing of 8.65%.Once we do that for all the states we end up with.
|Marginal Seat Swing||8.65||10.34||8.55||8.84||4.14|
|Safe gov Seat Swing||12.14||14.52||12.01||12.41||5.81|
|Safe ALP Seat Swing||7.45||8.91||7.37||7.61||3.56|
However, these swings are a little overblown. For instance, there are 48 seats in NSW. If we multiply those 48 seats by the NSW State vote of 9.2 (in the top table) we get 441.6 swing units. However, if we multiply the NSW marginal seat number by the NSW marginal seat vote, and do the same for the safe seats, we end up with 464.7 swing units. Hence the swing is slightly overcooked in the second table. So we’ll simply adjust the swings in the second table by the ratio of the swing units calculated in both tables e.g. Marginal seat swing in NSW = 8.65*(441.6/464.7) = 8.2
Doing this for all states gives us:
What is interesting here is that if we calculate the swing units horizontally rather than vertically using this table, what we find is that the estimated swings in the marginal and safe government seats are actually slightly smaller than the Newspoll estimate, and the Safe ALP swing is
a point or 2 higher less than a point higher than Newspoll estimated. But for our purpose here, which is to identify the seats the Newspoll quarterly suggests would change hands, our result will actually be a conservative estimate. We will essentially be underestimating the result.
[Update: calculating horizontally we end up with 8.03 vs. 8.3 for marginals, 10.8 vs. 11.6 for safe government seats and 7.2 vs. 7.1 for safe ALP seats]
Now we have our swings, we can simply apply them to the 139 seats and see what comes out.
There are 49 seats in total that would change hands according to Newspoll in these 5 states; 16 in NSW, 11 in QLD, 5 in SA, 2 in WA and an enormous 15 in Victoria (which gets back to my constant wondering about WTF is going on in Victoria over the last few weeks).
The results below show the Seat, the State its in, the ALP two party preferred result at the 2004 election (adjusted for the 2006 redistribution) and the projected Newspoll vote.
|Division||State||ALP 2004 TPP||Projected|
For the national total, you can add the two Tassie seats and Solomon from the NT for a total of 52 seats changing hands.
Getting back to why Victoria is acting unusually, that big swing has to be going somewhere. If we look at the ALP primary vote measured quarterly, in the 4 states that are swinging big we get:
It’s become a case of the rise and rise of Victoria, starting from the introduction of Workchoices at the beginning of the second quarter 2006.
There’s been a bit of confusion over how to read this, which is my fault for not explaining it properly.
This is just like the national pendulum where a certain swing, if it were uniform, would deliver so many seats.
The only difference is that this is 15 pendulums instead of one, where each State has 3 pendulums – marginal seats, safe government seats and safe ALP seats.
Just like the national pendulum, there will be seats that will swing less than the average swing, but as a result there will be other seats that will swing more than the average swing to balance out the weight of what makes up the “average swing”.
So if you see a few seats in the list above that give you a “Holy Smokes Batman” moment , it may be that the seat in question wasn’t (according to the Newspoll data) actually swinging that much, but other seats in its category would have to be swinging more than the average to take the weight.