Why do voters in single-party regimes express support for the ruling party in such large numbers? Scholars offer three sets of explanations: 1) Support is manipulated by regime leaders or falsified by frightened voters; 2) Support is due to genuine popularity or “performance legitimacy”; 3) The incumbent party holds an extreme incumbency advantage due to voters’ certainty about their candidates’ policy positions or access to state resources. Despite the impressive theoretical development in this literature, these arguments have not been subjected to a research design capable of examining the relative importance of each of these factors. We use a unique survey experiment on nearly 42,000 Vietnamese citizens over three years that reduces the threat of preference falsification and allows us to isolate voter's true preferences as much as possible. While we find some evidence for all three explanations, we find substantial support for incumbency bias. An important subset of Vietnamese voters—those inclined to vote for non-party candidates—sincerely favor the party under conditions of uncertainty about the candidates’ policy stances or experience in the legislature.

中文翻译：

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越南一党执政优势：公共选举支持的联合调查分析

为什么一党制政权的选民如此多地表达对执政党的支持？学者们给出了三套解释：1）支持被政权领导人操纵或被吓坏的选民伪造；2) 支持是由于真正的受欢迎程度或“表演合法性”；3）由于选民对其候选人的政策立场或获得国家资源的确定性，现任政党拥有极端的在职优势。尽管在该文献中取得了令人印象深刻的理论发展，但这些论点尚未经过能够检验这些因素中的每一个的相对重要性的研究设计。我们在三年内对近 42,000 名越南公民进行了一项独特的调查实验，以减少偏好伪造的威胁，并使我们能够尽可能地隔离选民的真实偏好。虽然我们找到了所有这三种解释的一些证据，但我们发现了对在职偏见的实质性支持。越南选民的重要子集——那些倾向于投票给无党派候选人的人——在候选人的政策立场或立法机构经验不确定的情况下真诚地支持该党。