Saturday, 15 February 2014

The Post-Mapstravaganza Clean-Up Party

Mapstravaganza comes to an end today. If you have not been following this weekend's binge on all things psephocartographic, you can find parts 1 and 2 on the other end of those links. It is advised that you read those first, as this post may contain some spoilers.


So far we have six maps:

Current standings

Average of seat histories since 1938
Average of seat histories since 1993
10% CDA (10% 2010 results, 9% 2006, 8.1% 2002 etc.)
Carry% VDTA (each layer determined by % of seats retained)
50% Carry% VDTA (as above, adjusted so top 4 layers have an average 50% opacity)
Maps 1, 2 and 6 are similar to those used in the federal election, although some methodological changes (e.g. 1938 cut off) were necessitated by the peculiarities of South Australian electoral history. The equation for map 6 has been modified from 7 layers to 4.

  1. A map of current seat incumbency. In the 2013 federal election the equivalent of Map 1 was found to be an 85% accurate predictive tool, and the carry% values calculated last post suggest a generally greater than 80% success rate at state level
  2. In the 2013 federal election the equivalent of Map 2 was also found to be 85% accurate
  3. Map 3 is a variation on Map 2 semi-arbitrarily defining 1993 as the start of modern electoral history due to the presence of a significant proportion of contemporary seats
  4. Map 4 is a new approach of unknown accuracy as a predictive tool. Ideologically it is a hybrid of Maps 2 and 6, both of which had well-performing equivalents in 2013
  5. Map 5 is useless and will not be dealt with beyond this point. It is a demonstration of VDTA techniques, but has high levels of opacity resulting in a map largely equivalent to an outdated Map 1 (i.e. 2006 incumbency map). This map is inferior to Map 1 and is therefore ignored.
  6. Is mathematically similar to a 2013 federal tool with 78% predictive success. Modifications to the underlying values for calculating the opacities have hopefully improved this, but may not have. This includes the shift from 7 to 4 layer direct influence (lower layers may still be influential in large numbers) which brings it into line with the 1993 origin of the modern political theatre suggested in Map 3


Normally I would save these tables for a data dump, but discussing them here means we do not need a data dump at all.

Good thing I didn't start blogging before the invention of computers, or I would have had to do this with paint chart names...

This table includes the colours of all five usable maps (along with their hex-codes for the number crunchers out there). Note that although there have been no green seats won in SA, their is still a green value for many of these colours. I'm going to assume that anyone who knows how to read hexidecimal colour codes also knows that white light is composed of every colour combined, and so this green is obviously leaking through from the white background. This is obviously also true for red and blue, so areas with more background colour (e.g. those seats with a shorter history) get less clear cut results - which is fitting because it means longer histories can provide more confidence in predictions.

Exactly how close to the red-blue balance a seat should get before it is considered too close to call is up for debate, but for simplicity and considering this is but one tool, I am calling every seat's trend pattern regardless of how close it is:

Colours exaggerated based on their relative red and blue values
The hope is that this approach will improve the overall accuracy by combining data. For example, if we assume each map is roughly 80% accurate, seats like Hartley or Morialta can be viewed as examples where one map's inaccuracy is corrected by the other four. By using multiple sources of roughly equal reliability the outliers can be isolated and dealt with; you would have to be really really unlucky to have the majority of the sources defective.

I make no apologies for basing my statistical methods on the works of Philip K. Dick
A couple of notes: None of these methods, with the possible exception of Map ! (current standings) really allow an Independent's strength to become fully apparent. Mount Gambier is the real outlier here, due entirely to never having been held by a party affiliated candidate.

Also, these methods look at trends and history. The idea of a 100% accurate predictive model is ridiculous, but doubly so one based solely on past elections. This post and its prequels completely ignore the specifics of the election campaigns about to unfold, and are perhaps best views as indicators of likely results in a perfectly balanced election.

This method reliably suggests Labor holds a slight advantage 25 seats, the Coalition has a head start in 18 and one is reliably called for a conservative independent in Mount Gambier (held by Independents Don Pegler and, before that, Rory McEwan).
This leaves Adelaide, Bright and Light as the three others.

Aggregate of Maps 1, 2, 3, 4 and 6. For simplicity, all maps are given equal weight.

On this balance Labor looks to have an advantage, requiring the Coalition to take two historical seats from Labor as well as gaining the Independent's support. But then there are historical seats and historical seats; taking Mawson would be a lot easier than taking Playford on this data, for example, since the former consistently hovers just on the red side of equal.

In reality, this Labor strength is largely the result of the long Labor incumbency. The trends point too a Labor win because that has been the history of this state for more than a decade. Therefore, while there may be a pro-Labor lean in the community at large, the tides may also turn quickly.

We will need to consult our other tools before making any confident predictions.

TL;DR: There are 5 useful maps from the past two days:
Map 1: Current standing of seats
Map 2: Averaged history since single-member electorates became universal in 1938
Map 3: Averaged history since the bulk of modern seats were contested in 1993
Map 4: 10% opacity layers of all elections since 1938, with new results eventually drowning out the old
Map 6: VDTA adjusted for 50% average opacity across the first 4 layers. Opacity of each layer depends on the reliability of that layer in predicting the following results.
Taking these as being equal in weight (adjustments to old systems and introduction of new methods make comparison of accuracy difficult anyhow), these suggest Labor has a strong history in 25 seats to the Coalition's 18.
These trends only reflect historical voting and may differ from the next election depending on campaign-specific events of a general shift in public opinion.

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