The victory forecast

Keen readers of this blog might recall that I wrote the following back in March:

The effect is that according to current trends, Yes will overtake No on the 1st of September 2013, and by the time of the referendum, there will be more than twice as many Yes voters as No voters.

Last Sunday, which was the day I had predicted the tables would turn, the only new opinion poll was one from YouGov that found a huge lead to the No side (but at the same time virtually unchanged compared to their previous polls); however, I must admit to feeling a bit anxious that my prophetic skills weren’t quite as sharp as I had hoped,

However, Monday morning I woke up to this press release from the SNP:

The most recently sampled independence referendum opinion poll puts support for Yes a point ahead of No — at 44 per cent to 43 per cent, with Don’t Know at 13 per cent — as we enter the month of a year to go until next September’s vote.

It’s somewhat frustrating being off by a day, but I still think it was a pretty decent prediction.

Perhaps this would be a good opportunity to update my prediction. Are we still on track for a 2-to-1 Yes victory?

If we do the same as in April, drawing a trend line through all the recent opinion polls, things aren’t looking too good at the moment; however this is heavily influenced by Sunday’s YouGov poll and Tuesday’s TNS one.

If we ignore the YouGov poll (there were multiple problems with it, as described here and here), and if we adjust the TNS poll to take the 2011 Holyrood votes in account (see this post by Calum Cashley), we’re still on track for a big Yes victory, although it probably won’t quite reach 2-to-1 territory.

I would have liked the polls to be converging at this point, but they clearly aren’t, so instead of producing a plot with new trend lines, I’ve added the newest polls to the old graph with the old trend lines. (I’ve added both the original and the adjusted versions of the TNS poll.)

It’s clear that the No vote share isn’t declining quite as fast as I predicted back in April, no matter which polls we look at. However, the Yes vote share is potentially rising faster than predicted (if we look only at the most optimistic polls).

Until we get to a point where the opinion polls start converging again, I think this is the best we can do. It’s definitely looking like a decisive Yes victory, but perhaps not quite as big a landslide as I thought in April.