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Does the Front-Runner Gain Ground? What Happens in the Last Week of the Campaign

In four of the five Spanish general elections since 2015, the party that led the final polls won more than the polls gave it, and so did the conservative People's Party (PP) and the Socialists (PSOE) combined: the vote concentrates at the end, mostly at the expense of the mid-sized party of the moment. But it is not a law. In 2023 the front-runner lost almost a point and the runner-up gained. And most of it happens when polls can no longer be published.

23 October 2026 · Miguel · Leer en español

From 24 to 28 November no poll may be published in Spain. This is the veda, the ban set by the electoral law for the five days before the vote. What happens in that last week is therefore the part we see least. We looked at what happened in the five general elections since 2015 using two sources: published polls, compared with the results, and the daily tracking done by the CIS (Spain’s state polling institute) during the July 2023 campaign.

The front-runner usually gains at the end, but not always

We compare the average of polls with fieldwork in the final seven days (including those published abroad during the ban) with the result.

Election Front-runner in the final polls Polls, last week Result Difference
2015 PP 26.8% 28.7% +1.9
2016 PP 29.5% 33.0% +3.5
April 2019 PSOE 27.6% 28.7% +1.1
November 2019 PSOE 27.2% 28.0% +0.8
2023 PP 33.9% 33.1% −0.8

In four of five elections, the party in first place won more than the final polls gave it: 1.3 points on average. This is often called the bandwagon effect. The exception is the most recent election: in 2023 the PP, which led every poll, won almost a point less.

Tactical voting: PP and PSOE together

The most repeated pattern is not about the front-runner but about the two big parties together.

Election PP + PSOE, last week Result Difference Who fell short of the polls
2015 47.4% 50.7% +3.3 Ciudadanos, a centre-right liberal party (−2.7)
2016 51.1% 55.6% +4.6 Unidos Podemos, a left-wing alliance to the PSOE’s left (−3.1), and Ciudadanos (−1.0)
April 2019 47.0% 45.4% −1.5 Vox, the far-right party (−1.8)
November 2019 47.4% 48.8% +1.4 Ciudadanos (−1.2) and Unidas Podemos (−0.8)
2023 62.3% 64.8% +2.5 Sumar, the left-wing platform to the PSOE’s left (−1.0), and Vox (−0.6)

In four of five elections, PP and PSOE together won more than the polls gave them: two points on average. Almost always this came at the expense of the mid-sized party of the moment: Ciudadanos in 2015, Podemos in 2016 or Sumar in 2023. This is what is known as tactical voting: voters who prefer a smaller party end up voting for the nearest big one, so that their vote counts or to stop a rival. The exception, April 2019, coincides with the collapse of the PP, which won 2.6 points less than the polls gave it.

One more fact, which we have already built into the model: the PSOE won more than the final polls gave it in all five elections (+1.4, +1.1, +1.1, +0.8 and +3.3 points).

The shift comes when there are no polls

Comparing last-week polls with those from one or two weeks earlier, they barely move. In 2016 the PP went from 29.4% to 29.5% and won 33.0%. In 2023 the PSOE went from 28.5% to 28.4% and won 31.7%. The shift does not show in campaign polls: it appears between the last poll and the ballot box.

With these data we cannot fully separate how much of that gap is a real last-minute change and how much is polling error, since polls have for years measured some electorates worse than others. But there is one source that lets us see movement inside a campaign.

What the CIS saw in July 2023, day by day

During the campaign for the 23 July election, the CIS conducted 27,058 interviews over nine fieldwork days, from 13 to 22 July (no fieldwork on Sunday 16). With the microdata we can follow the vote day by day. So that the result does not depend on whom the CIS happened to interview each day, we adjusted each day so that the recalled 2019 vote is the same every day. CIS levels are not reliable (it overstates Sumar and the PSOE), so we look only at changes.

Fieldwork days PP PSOE Sumar Vox Still undecided
13 to 15 July 30.4% 33.9% 16.3% 10.2% 8.8%
17 and 18 July 29.7% 34.1% 16.1% 10.7% 8.7%
19 and 20 July 27.6% 34.2% 17.3% 11.6% 7.9%
21 and 22 July 28.0% 32.8% 18.3% 11.8% 7.4%

Vote plus sympathy, as a share of declared valid votes. Margin of error for each day: about ±1.8 points; for each pair of days, about ±1.3.

Over the final ten days, the PP fell by about 2.5 points, mostly from 19 July, while Vox and Sumar rose slightly and the PSOE held steady. Undecided voters went from 9% to 7.4%. At the ballot box, the PP won less than the polls gave it and the PSOE quite a bit more. The PP’s fall shows in the tracking; the PSOE’s late rise does not, which suggests it came in the last days or from voters the survey does not capture well.

A reserve of tactical votes

The same survey asked each voter for a second choice. Among those planning to vote for Sumar, 66% had the PSOE as their second choice. Among Vox voters, 58% had the PP. This is the reserve that tactical voting draws on: voters who, if they end up believing their party is of no use, have already decided where to go.

What this means for 29 November

The altnalysis model does not add a bandwagon effect of its own. It does include industry error, with wide tails, and since this week it corrects half of the bias with which polls have underrated the PSOE in the last five general elections. If history repeats itself, the greater risk is for mid-sized parties: Vox and Frente Amplio (the new brand of the Sumar space) in provinces where they fight for the last seat. The PP and the PSOE would be the biggest gainers, but the front-runner does not always gain the most: in 2023 it was the other way round.

How we calculated it