The CIS estimates PSOE support at 34% and PP support at 22.2%. Several pollsters say the sample includes too many people recalling a PSOE vote in 2023; the institute says it weights recalled votes in its final estimates.
From 1 to 6 October, interviewers called 5,025 people across Spain for the CIS’s latest barometer. The full sample has a stated margin of error of ±1.4 percentage points. The poll puts the PSOE almost 12 points ahead of the PP, but several polling specialists say the result is weakened by an unusually high share of respondents who recall voting PSOE in 2023. The institute says its samples are random and representative, and that it weights recalled votes when calculating its final estimates.
The CIS estimates PSOE support at 34% and PP support at 22.2%, an 11.8-point gap. Vox stands at 17.1%. Sumar/Frente Amplio is at 6.1%, while Podemos is at 3.1%. On recalled vote, 38.2% say they voted PSOE in the last general election, compared with 19.5% who say they voted PP. In 2023, the PSOE received 31.6% of ballots and the PP 33%. Since September, the CIS estimate for the PSOE has risen from 31% to 34%; the PP’s has fallen from 25.5% to 22.2%.
One other result stands out.
Asked to place themselves on a scale from 1, the far left, to 10, the far right, 18.9% chose 1. Almost as many, 22%, chose 5, the centre.
Ignacio Urquizu, director of Metroscopia and a former Socialist MP, said recalled vote helps pollsters spot when a party is overrepresented in a sample. He said the mismatch at the CIS had grown and questioned an estimate that leaves the combined support for the PP and Vox below 40%. The CIS puts those parties at 39.3% together, against 40.1% for the PSOE and Sumar/Frente Amplio. Urquizu’s view is that a sample tilted towards PSOE voters makes the right-wing bloc look too small.
Belén Barreiro, director of 40dB. and a former CIS director, said the recalled-vote figure for the PSOE was very high. Her firm’s survey showed a figure 10 points lower. Barreiro argued that left-wing respondents may be more willing than right-wing voters to take part in interviews, and called the share of respondents placing themselves on the far left unusual compared with other surveys.
Francisco Camas, director of public research at Ipsos, described the sample as misaligned and inadequately corrected. He said left and centre-left voters are generally more willing to give their opinions in Spain and elsewhere. The CIS’s public reputation may also affect who agrees to be interviewed, he said. A sample imbalance can distort answers beyond voting intention, including views of political leaders and public concerns.
Camas also pointed to the poll’s voter-transfer figures. Although the CIS estimates PSOE support at 34%, three points above its 2023 result, only 64% of respondents who voted for the party say they would do so again. Five percent say they would switch to the PP, and 2% to Vox. Narciso Michavila, president of GAD3, said the recalled-vote data would imply the PSOE won 183 seats in 2023, rather than the 121 it actually secured.
Michavila also argued that Vox is the leading party among voters under 45. He said those voters would not be swayed by the Maricarmen housing case, whose disputed flat featured in an earlier report. That was part of his assessment of voter behaviour, not a finding from the CIS survey.
Other specialists challenged the sample. Sociologist María Ángeles Durán called the gap between the PSOE and PP surprising, but said she did not believe José Félix Tezanos was deliberately manipulating the figures. Alberto Penadés, a sociology professor at the University of Salamanca, said the imbalance between recalled PSOE and PP voters made him distrust the barometer. Political scientist Paco Llera questioned why the CIS had not corrected the recalled-vote bias in its estimates.
The CIS rejects the criticism. Its sources say responses are recorded literally and published as collected, while recalled vote is weighted in the final estimates. They also cite the long-established phenomenon of PP voters not disclosing their vote, and say recent interviews show greater willingness to respond to CIS surveys. The institute says its estimate reflects the period when interviews took place and is not, by itself, a forecast of the election result.
The fieldwork ran from 1 to 6 October, straddling Pedro Sánchez’s 5 October announcement that an early election would be held on 29 November. Interviews took place amid the housing crisis and after the cancellation of two government housing decrees. The CIS published its estimate about six weeks before the scheduled election. The Partido Popular responded by saying the CIS had lost all credibility.
