MRC/CSO Social & Public Health Sciences Unit, School of Health & Wellbeing, University of Glasgow, Glasgow, UK.
Res Synth Methods. 2024 Nov;15(6):826-838. doi: 10.1002/jrsm.1730. Epub 2024 Jun 22.
Bradford Hill (BH) viewpoints are widely used to assess causality in systematic reviews, but their application has often lacked reproducibility. We describe an approach for assessing causality within systematic reviews ('causal' reviews), illustrating its application to the topic of income inequality and health. Our approach draws on principles of process tracing, a method used for case study research, to harness BH viewpoints to judge evidence for causal claims.
In process tracing, a hypothesis may be confirmed by observing highly unique evidence and disconfirmed by observing highly definitive evidence. We drew on these principles to consider the value of finding supportive or contradictory evidence for each BH viewpoint characterised by its uniqueness and definitiveness.
In our exemplar systematic review, we hypothesised that income inequality adversely affects self-rated health and all-cause mortality. BH viewpoints 'analogy' and 'coherence' were excluded from the causal assessment because of their low uniqueness and low definitiveness. The 'experiment' viewpoint was considered highly unique and highly definitive, and thus could be particularly valuable. We propose five steps for using BH viewpoints in a 'causal' review: (1) define the hypothesis; (2) characterise each viewpoint; (3) specify the evidence expected for each BH viewpoint for a true or untrue hypothesis; (4) gather evidence for each viewpoint (e.g., systematic review meta-analyses, critical appraisal, background knowledge); (5) consider if each viewpoint was met (supportive evidence) or unmet (contradictory evidence).
Incorporating process tracing has the potential to provide transparency and structure when using BH viewpoints in 'causal' reviews.
布拉德福德·希尔（BH）观点被广泛用于系统评价中的因果关系评估，但它们的应用往往缺乏可重复性。我们描述了一种用于评估系统评价中因果关系的方法（“因果”评价），并举例说明了该方法在收入不平等与健康问题上的应用。我们的方法借鉴了案例研究中使用的过程追踪原则，利用 BH 观点来判断因果关系主张的证据。
在过程追踪中，一个假设可以通过观察高度独特的证据来证实，也可以通过观察高度明确的证据来证伪。我们借鉴了这些原则，考虑了为每个 BH 观点找到支持或矛盾证据的价值，这些观点的特征是独特性和明确性。
在我们的范例系统评价中，我们假设收入不平等会对自评健康和全因死亡率产生不利影响。由于 BH 观点“类推”和“一致性”的独特性和明确性较低，因此将其排除在因果评估之外。“实验”观点被认为是高度独特和高度明确的，因此可能特别有价值。我们提出了在“因果”评价中使用 BH 观点的五个步骤：（1）定义假设；（2）描述每个观点；（3）为真实或不真实的假设指定每个 BH 观点预期的证据；（4）为每个观点收集证据（例如，系统评价荟萃分析、批判性评价、背景知识）；（5）考虑每个观点是否得到满足（支持性证据）或未满足（矛盾性证据）。
在“因果”评价中使用 BH 观点时，纳入过程追踪有可能提供透明度和结构。
