The 2016 Spanish general election if it unfolded according to the Sigma Dos exit poll. This poll, which surveyed 132,000 voters, gave results for the centre-right People's Party (PP) and left-wing Unidos Podemos (UP) that were, respectively, about 4.5 points lower and 4.4 points higher than they actually turned out to be. Most polls in the final week of the campaign gave similar results. Unidos Podemos was widely expected to surpass the Spanish Socialist Workers' Party (PSOE), the traditional party of the centre-left; UP had been leading them in the polls since March. However, they suffered an unexpected decline in results from the previous election, losing 3.3 points and remaining in third place behind PSOE.
In this scenario, Unidos Podemos performs in line with expecations, increasing their seat tally by 24. This is due to a small swing in their favour combined with the alliance with the United Left, which had caused vote splitting issues in the previous election. Both PP and PSOE lose 6 seats, while liberal Ciudadanos suffer worst, losing 13 seats on a two-point swing. UP and PSOE now hold a majority between them, and government talks proceed; Pablo Iglesias, leader of Unidos Podemos, is eventually elected Prime Minister. He becomes the first Prime Minister since 1982 not to come from either PSOE or PP.