Evaluating Effectiveness Qualitatively: A Systematic Review and Synthesis of Methods Applied in Intervention Research

Introduction. Sole reliance on quantitative data for intervention evaluation has been criticised extensively, and informed stakeholder decision-making is now widely recognized as requiring diverse sources of evidence. Qualitative research provides a more nuanced understanding of how and under what circumstances interventions work, and invites diverse voices and expertise into the evaluation process. It offers a methodologically pluralist toolbox for collecting and synthesising these insights. Within this, diverse qualitative methodologies for evaluating effectiveness have been developed to contribute to evidence-based practice. A systematic account of these methodologies is currently lacking, however. 

Goals and methods. The aim of the current systematic review was to gauge the landscape of the currently applied qualitative methodologies designed to evaluate psychosocial interventions and enhance decision-making in this sector. Based on a systematic search of qualitative studies, this review maps the evolution of the methods currently in use from their conceptualizations to eventual applications. A comparative taxonomy of qualitative evaluation methods is developed based on data extraction and interpretation, and content analysis is used to examine the factors for their differential application in practice to identify best practices moving forward. 

Expected results. The review shows the variety of methods and method applications, often linked to difficulties in application, lack of methodological guidance, thin descriptions of original methods, and the inherently ideographical nature of qualitative research. Common omissions and modifications are examined, with reasons stated for alterations highlighted.

Conclusions. Qualitative research offers a variety of frameworks for appraising psychosocial intervention effectiveness, complementing and extending the goals and means of quantitative research. The methods reflect a variety of epistemological, ontological, analytical, and synthetic orientations, enabling them to address a range of evaluation goals. Considering the existing theoretical models for evaluating qualitative evidence on par with their practical applications would allow for broadening the methodological and evidentiary base.