Background: identifying the ‘critical ingredients’ and contextual moderators of complex interventions is often challenging for review authors. Nevertheless, determining the detail of which intervention components to favour in which situations is essential for decision makers seeking to implement review findings. Qualitative Comparative Analysis (QCA) is a promising new review method for examining the ‘causal recipes’ of complex interventions. The diversity of ways in which QCA can provide a useful analytical lens in systematic reviews continues to emerge. We present two different analyses using QCA in a review on interventions to increase the uptake of influenza vaccines among healthcare workers.
Objectives: to provide a worked example of how QCA can be used in diverse ways to provide a robust, systematic and transparent evaluation of intervention complexity.
Methods: an existing review on interventions to increase flu vaccination uptake among healthcare workers found variation in interventions and outcomes. Despite noting some overarching patterns the review authors concluded that the remaining ‘substantial heterogeneity’ required further analysis. We noted opportunities for two different types of analysis using QCA. The first was used to explore the nature of successful interventions. The review had found ‘hard mandate’ policies involving severe sanctions such as loss of employment to be the most successful approach for increasing vaccination uptake. Nevertheless, there was substantial heterogeneity in the nature and outcomes of hard mandates. The second analysis we performed sought to identify the nature of unsuccessful interventions. Interventions other than hard mandates were felt to be more palatable and easier to implement, but were generally less successful and tended to rely on single components such as education, improved access and awareness-raising rather than using a diversity of approaches. By using QCA to explore the nature of the least effective of these other interventions we aimed to provide useful detail about intervention configurations that decision makers should avoid wasting resources on. This analysis was guided by an existing synthesis of healthcare workers' perceptions and experiences of vaccination for seasonal influenza.
Results: we were able to use QCA in this review to identify critical ingredients both for successful hard-mandate policies and for unsuccessful vaccination policies. These different approaches provide useful detail for decision makers about where to invest resources and where to avoid investing resources.
Conclusions: there is diversity in the ways that QCA can be used to unpack intervention complexity to assist decision makers.
Patient or healthcare consumer involvement: the analyses were guided by the perceptions of healthcare workers through use of an existing qualitative evidence synthesis.