Several scholars have observed persistent gaps between policy responses to complex, ambiguous and politicized problems (such as migration, climate change and the recent Covid-19 pandemic) and evidence or ‘facts’. While most existing explanations for this ‘evidence-policy gap’ in the migration policy field focus on knowledge availability and knowledge use by policymakers, this article shifts the focus to processes of knowledge formation, exploring the questions of what counts as ‘evidence’ for migration policymakers and what are the sources of information that shape their understandings of migration policy issues. It does so, by developing a network-centred approach and focusing on elite US policy-makers in the field of irregular and asylum-seeking migration. This ‘heuristic case’ is used to challenge existing explanations of the ‘evidence-policy gap’ and to generate new explanations to be tested in future research. Our findings—based on qualitative and quantitative data collected in 2015–2018 through 57 elite interviews analysed applying social network analysis and qualitative content analysis—challenge scholarly claims about policymakers’ lack of access to evidence about migration. We also challenge claims that migration-related decision-making processes are irrational or merely driven by political interests, showing that policymakers rationally collect information, select sources and attribute different relevance to ‘evidence’ acquired. We instead highlight that knowledge acquisition processes by elite policymakers are decisively shaped by dynamics of trust and perceptions of political and organizational like-mindedness among actors, and that political and ideological factors determine what qualifies as 'evidence' in the first place.

一些学者观察到，对复杂、模糊和政治化问题（例如移民、气候变化和最近的 Covid-19 大流行）的政策反应与证据或“事实”之间持续存在差距。虽然移民政策领域对这种“证据与政策差距”的大多数现有解释都集中在政策制定者的知识可用性和知识使用上，但本文将重点转向知识形成过程，探讨什么算作移民“证据”的问题政策制定者以及影响他们对移民政策问题理解的信息来源是什么。为此，它制定了一种以网络为中心的方法，并重点关注非正常移民和寻求庇护移民领域的美国精英政策制定者。这种“启发式案例”用于挑战“证据与政策差距”的现有解释，并产生新的解释以在未来的研究中进行测试。我们的研究结果基于 2015 年至 2018 年通过 57 名精英访谈收集的定性和定量数据，并应用社交网络分析和定性内容分析进行分析，挑战了学术界关于政策制定者缺乏获得移民证据的说法。我们还对有关移民相关决策过程不合理或仅受政治利益驱动的说法提出质疑，这表明政策制定者理性地收集信息、选择来源并对所获得的“证据”赋予不同的相关性。相反，我们强调，精英政策制定者的知识获取过程是由行为者之间的信任动态以及对政治和组织志同道合的看法决定性地决定的，而政治和意识形态因素首先决定了什么是“证据”。