Testing for saturation in qualitative evidence syntheses: An update of HIV adherence in Africa

A systematic review of randomised trials may be conclusive signalling no further research is needed; or identify gaps requiring further research that may then be included in review updates. In qualitative evidence synthesis (QES), the rationale, triggers, and methods for updating are less clear cut. We updated a QES on adherence to anti-retroviral treatment to examine if thematic saturation renders additional research redundant.

We adopted the original review search strategy and eligibility criteria to identify studies in the subsequent three years. We assessed studies for conceptual detail, categorised as 'rich' or 'sparse', coding the rich studies. We sought new codes, and appraised whether findings confirmed, extended, enriched, or refuted existing themes. Finally, we examined if the analysis impacted on the original conceptual model.

After screening 3895 articles, 301 studies met the inclusion criteria. Rich findings from Africa were available in 82 studies; 146 studies were sparse, contained no additional information on specific populations, and did not contribute to the analysis. New studies enriched our understanding on the relationship between external and internal factors influencing adherence, confirming, extending and enriching the existing themes. Despite careful evaluation of the new literature, we did not identify any new themes, and found no studies that refuted our theory.

Updating an existing QES using the original question confirmed and sometimes enriched evidence within themes but made little or no substantive difference to the theory and overall findings of the original review. We propose this illustrates thematic saturation. We propose a thoughtful approach before embarking on a QES update, and our work underlines the importance of QES priority areas where further primary research may help, and areas where further studies may be redundant.