Scorecard on my general election predictions is D- and the lesson learned is GIGO

The other day I made a series of general election predictions, and in the spirit of self-flagellatory repentance I will score myself. So here goes…..

Vote Share – what I said about Labour and Tories: Labour vote share will be 0.5% higher than the Poll of Polls to reflect the better ground operations of Labour, and the Conservatives will be correspondingly 0.5% lower. [This would have given Lab = 33.8% and Con = 33.2%]

The actual vote share was: Lab = 30.9% and Con = 36.9%. This is a fail and gets no marks.

On Ukip vote share I said: Ukip vote share will go up on the Poll of Polls vote share because of the “shy Ukippers” who don’t like to tell pollsters they will vote Ukip. But they will also lose vote share because of their much poorer GOTV operation. Overall these two things will cancel out and mean their vote share is as per the Poll of Polls. [This is 13.4%]

The actual vote share was: Ukip = 12.6%. This is not a total fail and is worth a mark.

On Scotland I said: As with the “shy Ukipper” effect in England there will be a “shy Labour” affect in Scotland (similar to the “shy no” in the independence referendum) which along with tactical voting will mean Labour won’t suffer total wipe out and get between 3 and 7 seats.

The actual result was: Labour won one seat. Not a total fail but only just worth a generous half a mark for it not being total wipe out for Labour.

Shock # 1 predicted was Alex Salmond: Alex Salmond will get run very close in Gordon. I predict whoever wins will have a majority less than 1,000.

What happened: He won convincingly by over 6,000 votes increasing the share of the vote. My prediction was way off and gets no marks.

Shock # 2 predicted on the Lib Dems: Clegg will hold his seat but end up being removed as Lib Dem leader after the Lib Dems end up with fewer than 25 seats and what remains of his party disagree with his attempts to form a coalition with the Conservatives.

What happened: Clegg held his seat, the Lib Dems dropped to 8 seats, and Clegg is no longer leader but for different reasons to my prediction. I’ll be very generous and award myself half a mark.

Shock #3 with Farage: Farage will not win his seat.

What happened: The only prediction I got totally right.

I would give myself a very generous D- for getting a few of the more minor predictions close, but on the big prediction, the Lab-Con vote share, it was an abject fail. So overall it has to be a fail, hence the D-.

Before becoming a trade union official I worked for 10 years as an engineer. I became quite proficient at monitoring engineering data and then analysing it through different mathematical models. One acronym I always kept in mind (one that all data analysts will know) is GIGO – Garbage In, Garbage Out.

I believe the methodology of the Polls of the Polls mathematical model was sound, but the information put into the model (the results of the opinion polls) was clearly garbage and I should have remembered GIGO as a possible source of error.

The only thing that spares my blushes is that so many other people got it wrong too. But this guy actually did predict the Shy Tory phenomenon based on looking at opinion polls and actual election results going back 50 years. He identified a number of issues, one of the most crucial being a tendency of the opinion polls to overstate Labour and understate the Conservatives.

His blog post (done before the election was held) is a must read for anyone wanting to understand what went on.

For my part I will stick to my general maxim when a predictive model is shown to be so badly wrong, I will only ever put any faith in it if there is strong evidence that suitable steps have been taken to correct the fundamental flaws. Given the true test of a predictive model is the real outcome it is trying to predict, it’s going to be hard to believe any opinion polls until they are judged against the outcome of the 2020 general election.


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