Continuing with the Good Judgment Project mentioned in the previous post, I made some predictions about the Taiwan election (before the day of the election, of course). Frankly, the outcome of the presidential race never had confidence intervals large enough to make things interesting. Fortunately, the GJP assignment is to predict seat distribution of the Legislaive Yuan (LY), which is believed to be a tighter race than the presidency.
A short summary: I got lucky with my rough analysis. I predicted 65 seats for DPP, 35 for KMT, with 13 taken by other parties. The results were 68 for DPP, 35 for KMT, and 10 for other parties. My predictions were very close.
Numerous polls conducted by media and polling companies showed that in the past one to two years, the electorate has been deeply unsatisfied with the ruling KMT government. The numbers have been generally stable, with dissatisfaction over 50% and satisfaction at less than 30%. While this does not bode well for the nationalists, I realized this could make prediction accuracy a little higher.
My idea was to study the pattern of the various Taiwan elections of the past couple of years, and applying them to the current election in 2016.
I have two choices: the 2012 LY election or the 2014 regional election. At first it may be obvious to choose the 2012 LY election, since we are predicting another LY election in 2016; however, the regional election had the advantage of being much closer to the actual 2016 election date, which minimizes variation, especially since our strategy is to extrapolate old results to this new one. The general atmosphere of the 2014 election is much more similar to 2016 than the 2012 election. It took place after the Sunflower movement and the occupation of the Yuan, an event that caused the approval rating of the government to tumble. Since then, the government's approval rate has stabilized. For this reason, I decided to analyze the 2014 election.
Opinion polls data are available on Wikipedia under the page "2014年中華民國直轄市長選舉及縣市長選舉". In summary, the DPP performed significantly better than expected by pundits and won a landslide. After going through each county and city, calculating the average difference between the polls and the final election results, the final results ended up being a whooping 18% higher on average than the polls suggested. Furthermore, in races where the results were close (difference less than 10%), the DPP performed 23% better. This wave of unexpected support resulted in the DPP snatching a good number of seats in traditionally KMT strongholds.
So how to explain such a large difference? If we assume the polls were accurate, and no committed voter changed
his/her mind, then that means around 2/3 of voters who were uncommitted in
the polls were won over by the DPP in the final moments of the
election (On average, 30% of respondents to pollsters were undecided). Since studies consistently showed that generally sizable
number of voters decide only toward the end of the election, it would not be a surprise to see another last minute surge, especially given the great similarity between the general mood between these two elections.
The final aggregate numbers from the polls just before the polling blackout period (which is roughly a week before the election) indicate DPP support at 31%, KMT at 18%, and undecided at 24%.
Therefore, assuming 2/3 of undecided voter go with the DPP, we may see actual DPP support over 45%. This is a little more
than KMT support in the 2012 Legislative Yuan elections, in which they won
64 seats.
The LY consists of members directly elected based on popular vote, and members elected in districts based on first-past-the-post. Of the 64 seats won by the KMT in 2012, only 16 are directly elected members, the rest coming from local districts. I am not familiar
enough with Taiwan to make any district-by-district analysis; however, past elections show that KMT has a wider spread of support than the DPP, meaning DPP support tends to be clustered in certain regions. The implication here is that the DPP needs a larger share of the popular vote to win the same number of seats as the KMT.
However, I predicted that this disadvantage is offset by the phenomenon of strong DPP surge in close districts observed in 2014. It is difficult to quantify how much effect this would have without going into a district by district analysis. I roughly estimated this would even out the disadvantage for the DPP due to the more clustered support base.
In the end, based on the extrapolated popular support data, the DPP should win roughly the same number of seats as the KMT did in 2012 (65 seats). KMT support this year is even lower than DPP in 2012, when they won 40 seats, so I pegged KMT seats at 35 (a lucky guess!). People First Party support seems stagnant, so major seat change is not expected. The additional support bled away by the KMT should be picked up by the new New Power Party, according to polling data, which should let them gain around 5 seats.
The final results were very close to my prediction, with DPP winning 68, KMT at 35, NPP at 5, and PFP at 3. The result affirms my presupposition that popular mood remains the same as in 2014, and the same mood among the electorate produces the same result. The prediction would have been significantly more difficult if a major shift in opinion was detected by pollsters.