In the last general election, two years ago, we saw that even though the polls all pointed to a dead heat, other data could help to predict a Conservative victory.

History may not repeat itself, but something similar may be true today: we perhaps should not get too carried away with opinion polls showing the race is getting closer.

Other indicators, such as historical polling bias, the personal ratings for the leaders and local election results are all a useful cross-check on the polling numbers.

The exact analysis I did in 2015 cannot be repeated in the same form, because of the short parliament. But with minor modifications, I have produced something similar.

Starting with historical bias, the Conservatives generally perform better at the ballot box than the polls suggest, and Labour tends to do worse. Only once in the last half-century have the Tories won a lower share of the vote than the average of final polls suggested.

But that example came in 1983, an election that looks quite similar to this one, in which Margaret Thatcher looked on course for a landslide against radically leftwing opposition. In the end, she won by less than predicted. With that in mind, the effect is probably neutral on this race.

In addition, polling methodologies have been revised since 2015, although the nature and extent of the changes varies between organisations. Pollsters privately (and in some cases, publicly) continue to express doubts about their samples.

How the party leaders are seen by the public is also important.

Comparing the percentages satisfied with the way the prime minister and the leader of the opposition are doing their jobs in the long-running Ipsos Mori series shows a reduced (but still substantial) 24-point lead for Theresa May. That does not mean we should expect the Conservative vote margin to be 24 points; it is more indicative of a lead of just over half of that.

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Finally, the local election results were extremely good for the Conservatives. This is a key part of the model because it does not rely at all on polling.

Both projections of how Great Britain would have voted had there been council elections everywhere show an 11pt win for the Tories, a much bigger margin than Margaret Thatcher won ahead of the 1983 and 1987 elections.

Because governing parties usually perform better in general elections than local elections, the results are more consistent with where the polls were during the first half of the campaign, than the single-digit gaps in some of the most recent polls.

Adding these three factors together and combining them into a single index, the likeliest outcome appears to be a Tory lead in the mid-teens; clearly at the higher end of the latest batch of polls, but with the risks to polling accuracy looking more balanced than two years ago.

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Events in the past few weeks of the campaign, such as the embarrassing U-turn by Theresa May on social care, or the terrorist attack in Manchester, could possibly have an impact on the result.

But the historical strength of the relationship between fundamentals and results suggests that events tend to have a more limited impact than political junkies often assume.

It would be foolish to pretend that they do not have any effect, but the limited evidence so far suggests Mrs May’s personal ratings have not changed much since the manifesto launch, though it is worth keeping an eye on them.

At this point, the likeliest outcome is that the Conservatives win convincingly.

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