The final resolution of the New Zealand Parliament a few
weeks back once again bucked my predictions for another term of conservative
government, proving that however hard predicting an election may be it’s
nothing compared to the uncertainty that follows once politicians come to power.
With any luck we will fare a little better in calling the
Queensland election on the 25th of this month. Before then, however,
we will have the results of the same-sex marriage poll released on Wednesday,
so we should have a quick look at that.
Voter Response Rate
Firstly, here is a graph for the rate of return of the
survey papers.
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| Polling dated from the last day of data collection. |
Generally, these types of polls have a margin of error in
the realm of 2-3 percentage points. There are two outliers from October 2nd,
however, that are well beyond this (marked in red). These results by Newgate
Research and ReachTEL suggested 77% and 79% of eligible voters had returned
their survey forms, about 30 percentage points higher than the previous day’s
result from Essential (47%) and higher than all subsequent polls but the final one,
taken one day before submissions closed.
There are many other hints that this data may be in error.
The article
publishing the Newgate Research figure included scepticism from Australian
Christian Lobby’s director, who said the 77% figure “would surprise me”, while
the source for the ReachTEL poll reported a suspiciously low 17.5% ‘No’
response. Crucially, these two polls were the only two (excluding the very
first and very last) during the survey that did not ask the likelihood of
voting from those who had not returned their ballots. The 77% and 79% figures
are also in the ballpark of those who intended to vote in the polls
taken prior to the survey beginning. I suspect, therefore, that these high
numbers capture not only actually returned ballots but those who intended to
return them—perhaps people who had filled out the papers and sealed them in the
envelope but not yet posted them.
Whatever the reason, we will ignore these two figures going
forward.
Conveniently, this line always trends positively now that
the outliers have been removed, which makes sense as no one should be able to
un-post their papers.
Voter Response
The latest data from Essential (see page 13)
suggests that 64% of people who voted ticked ‘Yes’, almost double the combined ‘No’
and ‘Prefer not to say’ votes.
While polling has had some embarrassing moments over the
last couple of years, at times wildly diverging from the actual results, this
data, being based on historical fact and not subject to change like opinion, should
in theory be a reliable indicator of the result.
Nevertheless, for the fun of it, let’s look at some other data
collected to predict a result.
Here is a graph of support for the ‘Yes’ and the ‘No’ camps,
ignoring the undecided vote (where recorded) as people either likely to not
vote, or to split broadly along similar lines to those who answered:
 |
| Polling dated from the last day of data collection. Ipsos poll (9/11/2017) omitted for uncertainty. Results for dates with multiple polls are averaged. |
Including the undecided/rather not say/other among polls
where ‘Yes’+’No’ < 100%, the graph is similar:
This data
however, is a mix of polls from people who have already voted, intend to vote
or both. We can separate out some of this data accordingly:
Although voting intention seems to fluctuate dramatically, actual
results seem to be quite flat and featureless compared to the preceding graphs.
The available data for these graphs only begins from the start of October
which, according to our very first graph, is after half of the submissions were
already cast. This gave a sizable fixed baseline, which fluctuations in slowly
accruing votes then had little impact upon.
Overall, there is a slight growth in the ‘No’ vote later in
the survey, but not a particularly concerning one for the ‘Yes’ campaign.
The ‘other’ data among those who have already voted,
presumably declining to answer rather than ‘don’t know’ as may surveys put it, is
reasonably constant. By comparison, the ‘other’ among those yet to vote grows
over time. This probably does not reflect voter’s wavering so much as a
proportional reduction in people intending to vote. As more votes were cast those
not intending to vote became a larger proportion of people in this graph.
All of the graphs examined so far would indicate a safe win
for the ‘Yes’ camp, with ‘No’ never exceeding 50% and only getting close
towards the final weeks of the survey among those yet to vote. By the end of
the yet-to-vote graphs (22/10/2017) 75% of eligible votes had already been returned.
A further 9% would be sent after this date, limiting the impact of this (comparatively)
high ‘No’ support.
Two More Graphs
With these last four graphs, we can calculate an approximate
value for ‘Yes’ and ‘No’ support over any given period from the slope of the dividing
line(s).
For the sake of producing something more than mere graphs of
publicly available data, here is a table of the daily support for ‘Yes’, ‘No’
and ‘Other’ (‘?’) extrapolated from the known polls (in grey):
And here is a table of the incremental increase in surveys
returned over time:
The listed averages have been chosen to align with known points
in the increase of surveys returned. Prior to October 1, at least 50% of the
returned surveys had voted ‘Yes’. 18% of eligible voters replied between then
and October 15, with a calculated average ‘Yes’ vote of 48.13%. 2% of forms were
posted in the following 24 hours according to the polls (remembering these dates
are somewhat artificial as they are collected over several days), at a
calculated 50.13% ‘Yes’. The next 8% before October 22nd had 57.75%
voting ‘Yes’. Similar information can be determined for the declared ‘No’ votes
and the unknown ‘?’s:
A similar graph can be constructed based on reported surveys
returned, but the simpler way to do this is to simply multiply the percentage
of returned votes by the percentage that were ‘Yes’, ‘No’ or ‘?’ like so:
Which yields:
Conclusion
All of the polling throughout the survey has indicated a win
for the ‘Yes’ campaign, and polling from the penultimate day of voting reports a
64% ‘Yes’ response—higher if some of the undeclared votes are also ‘Yes’.
According to the final graph above, this not only makes ‘Yes’ more than 50% of
the returned votes, but more than 50% of the issued votes. In other words
the ‘Yes’ result would be greater than the ‘No’ result (including all
undeclared votes) and the ‘did not answer’s combined.
Previous experience, particularly the British experience
with Brexit, has left me a little wary of polling. It is tempting to suspect a
hidden vote as we saw in the US presidential race, the Brexit vote and the UK
general election. These hidden votes came from both left and right, but always in
favour of the underdog, as though people were ashamed to admit they were voting
for the less popular option.
On the other hand, over-cautiousness about this exact issue
proved unfounded in New Zealand. In NZ, the people expected to vote voted. In
the other elections we saw an atypical and unpredicted surge in voters from the
disenfranchised working classes voting for Trump, whipped-up nationalists
voting for Brexit and politically engaged youth voting for Corbin. The
question, then, becomes one of whether we’ve been polling the right
demographics in the right proportions, something we cannot know until Wednesday’s
result.
However, there are two good reasons in my mind to trust the
polling in this case. Firstly, most of the polls offered an option to remain uncommitted
or not answer. This allowed a pollster-shy voter base to be captured without declaring
their position. If there is a hiding ‘No’ vote I would expect it to be mostly
contained in the thin grey bar in the above graphs.
The second reason I trust the polling data is that this is
not an election held on one day. Unlike all of the bad-polling examples, this
vote was conducted over almost two months. As a result we not only have data on
how people intend to vote, but on how they claim they actually did vote.
This data is free from late-season changes in attitude or people intending to
vote not getting around to it.
That said, completely aside from any science or reason, I will
slightly hedge towards a stronger-than-expected ‘No’ vote based on nothing but
gut feeling. The last polling has ‘No’ at 31%, plus a 5% undisclosed result. If
this all went to ‘No’ it’d be a 64:36 (or 16:9) victory for the Yes camp. I’ll
go a little further still and predict something in the order of 61:39, but
nevertheless by all accounts including my own, we should see a clear ‘Yes’
result on Wednesday.
