BARCELONA, Spain (AP) — Spain is preparing to hold its third parliamentary election in less than four years. But even though the exercise is familiar, uncertainty surrounds the election's outcome.

Polls indicate a substantial share of voters, about one-third, hadn't decided by the final week of campaigning how they would mark their ballots on Sunday.

Socialist Prime Minister Pedro Sánchez is hoping for a strong mandate to stay in the office he assumed 11 months ago when a no-confidence vote ousted his conservative predecessor.

A rising populist party also confounds confident predictions at the other end of the ideological spectrum. The Vox party is expected to give the lower chamber of the Spanish parliament its first lawmakers from the far right since the 1980s.

Aritz Parra contributed to this report from Madrid.