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Qualitative Comparative Analysis

Qualitative Comparative Analysis: A worked example to explore why some weight management interventions worked better than others.

Complex interventions, i.e. those with multiple interacting components and multiple potential moderators are common in healthcare. Interventions such as weight management programmes (WMPs) are particularly complex because they are social in nature; intervention impacts will likely be affected by the nature and beliefs of both the provider and the recipient of the intervention.

Statistical methods for synthesising evidence of effectiveness depend on intervention replication in order to operate effectively. For syntheses in which each intervention may differ from another (in sometimes unknown ways), they are less suitable. By contrast, Qualitative Comparative Analysis (QCA), an approach which has recently been employed in systematic reviews, makes use of the inherent variance in complex interventions. QCA seeks to answer a different question to that asked by previous reviews, i.e. rather than ‘what works, on average’, it aims to understand the mechanisms through which different interventions have the impact that they do. QCA systematically identifies configurations, or combinations, of various intervention and other contextual characteristics that are (or are not) present when an intervention has been successful (or not) in obtaining a desired outcome. QCA allows for multiple overlapping pathways to causality, and it identifies combinations of conditions as opposed to isolating the effects of single characteristics on intervention effectiveness. This may better represent the complex causal pathways that often characterise complex social interventions.

Despite extensive research effort which shows that WMPs that target diet and exercise are broadly effective, researchers have been unable to identify the critical features of such programmes. This session will use a worked example to outline the process of conducting a QCA and illustrate how the method was able to identify critical components of weight management interventions where other methods had been unsuccessful.