A week from today ,on Thursday 18 September, 2014, the people of Scotland
will have the opportunity to vote on whether Scotland should be an independent
country. As it is expected polling companies have measured public opinion in
order to assess whether or not Scots will vote in favor or against in the
referendum.
When
we look at all the polling data publicly available[i] we
can see that throughout the past two years most polls have given the No a majority (close to 50%), while the “Yes” option (for independence) has seen an average of support around 37% of interviewees (see figure 1). Of course the tendency over time has changed and the polls have gotten increasingly close in the last month.
Figure
1
Given
that what is important is to try to figure out the outcome come September 18th
we need to see the evolution of this polling data, and to average of
these polls. In order to average the polls we need to consider that each poll
is different, and more importantly that each polling house proceeds differently
to survey the public and weight the responses. As such I used a statistical
technique to average the polls which takes into account these differences[ii].
Figure 2 plots all the available
polls (in red the No option and in blue the Yes) without considering non
respondents. The blue and red line show the evolution of the averaging of the
polls. As it can be seen the gap, which was very wide for a long time has
considerably narrowed in the last month. And while the ‘Yes, Scotland’ campaign
is still losing the difference is less than 4 percentage points (Yes: 48.35% ;
No: 51,65%).
Figure 2
Just
to end the analysis, it is worth noting that despite the differences in
methodologies between the different polling houses currently polling scots,
there doesn’t seem to be any major biases. In fact, according to the estimation
no house has a bias significantly different than zero (figure 3); which is not
necessarily the case all the time and means that there is overall agreement
between all polling houses and where the trend line is.
Figure 3
[i] Sources
of survey data:
[ii] This
analysis is based on the “polling of the polls” technique introduced by Jackman ( 2005).
