Synthesize included studies

At the synthesis stage, results from included qualitative (QL) and quantitative (QT) studies are combined and interpreted. Several synthesis methods have been developed over the past decades such as meta-analysis, thematic synthesis, framework synthesis, critical interpretive synthesi, realist synthesis and meta-narrative synthesis. 


We conducted a review on mixed studies reviews to identify the type of synthesis designs used.  Based on typical mixed methods research designs, we found two main types of synthesis designs: sequential and convergent. The choice of the design depends on the review question(s). The resutls of this review are published in this paper: Hong QN, Pluye P, Bujold M, Wassef M. Convergent and sequential synthesis designs: Implications for conducting and reporting systematic reviews of qualitative and quantitative evidence. Syst Rev. 2017;6(61):1-14. 



1) Sequential synthesis designs


In the sequential synthesis design, the results of the synthesis of phase 1 inform the synthesis of phase 2. The integration occurs between the two phases. 


Example adapted from Mills et al. (2006)

Phases Review question Output
Phase 1  Qualitative question: What are the concerns of patients with cancer about, and the barriers to, participation in clinical trials?  3 main types of barriers to participaions in clinical trials
Phase 2 Quantitative questions:  What is the prevalence of these barriers? List of barriers commonly reported 

The QT studies identified only a few of the barriers compared with QL studies, suggesting that key issues should be incorporated into subsequent quantitative studies.


Some mixed studies reviews that used a sequential synthesis design: 


2) Convergent synthesis designs


In the convergent synthesis design, the syntheses do not depend on the results of each other and the data are synthetized in a complementary manner. In the convergent synthesis designs, we found that the integration can occur at 3 different levels: extracted data, synthesis results and discussion.   


A) Integration at the level of extracted data

This design was named data-based convergent synthesis design because all the extracted data (i.e., results from the qualitative and quantitative studies included in a review) are anlaysed using a same synthesis method. Also, the results of the synthesis is presented together in the results section. In this synthesis design, either qualitative or quantitative synthesis methods are used to analyse all the data.  When using qualitative synthesis methods, the results of qualitative, quantitative, and mixed methods studies are transformed into themes such as constructs, concepts and factors. This is called qualitization of the data. Here are some qualitative synthesis methods: thematic synthesis, realist review, critical interpretive synthesis, meta-narrative synthesis, and multiple case synthesis.  When using quantitative synthesis methods, the results of qualitative, quantitative, and mixed methods studies are transformed into variables and values. This is called quantization of the data. Examples of quantitative synthesis methods: content analysis, Bayesian synthesis, and configurational comparative method. 



Example of qualitative data-based convergent synthesis design, adapted from Bélanger et al. (2011)

Review question



Qualitative question: What are the (types of or key) processes of making shared decisions with palliative care patients?

Themes of qualitative studies (or qualitative part of mixed methods studies) are identified.


Variables used in quantitative studies (or quantitative part of mixed methods studies) are open coded qualitatively.


Then categories are developed.

Types of processes involved in shared decision making


Some mixed studies reviews that used a data-based convergent synthesis design: 


B) Integration at the level of the results of the synthesis 

This design was named result-based convergent synthesis design. In this synthesis design the QL and QT extracted data are analysed separately using a same or different synthesis methods and then the results of both synthesis are combined in a third synthesis (e.g., performing juxtaposition of the resutls of the synthesis, doing side-by-side comparison).  The synthesis methods used can be only qualitative, only quantitative, or mixed (i.e., using both qualitative and quantitative synthesis methods within a same review).  



Example of result-based convergent synthesis design, adapted from Campbell et al. (2011)

Review question


Quantitative question: For pregnant women, do diet and physical activity interventions prevent excessive gestational weight gain compared no intervention (e.g., routine prenatal care)?


Effect size

Qualitative question:  What are the viewpoints of pregnant women with regard to types of factors associated with the implementation and outcomes of diet and physical activity interventions preventing excessive gestational weight gain?

Three major themes relating to women's views of weight management in pregnancy


Explanation of the success or failure of the intervention


Some mixed studies reviews that used a result-based convergent synthesis design: 


C) Integration at the level of the discussion

This design was named parallel-results convergent synthesis design. It is similar to the previous design in which all the QL and QT extracted data are analysed separately using a same or different synthesis methods. However, the resutls of both synthesis are not compared in the results section.  Usually, the integration will occur in the discussion by interpreting the results of the syntheses.  


This design was observed mainly in health technology assessments (HTA) in which several review questions are asked (e.g., questions related to the effectiveness, cost-effectivess, acceptability, views, needs). Each review question was addresed separately and no attempt to combine the results of each synthesis was performed.  Usually, in the discussion, the recommendations will take account of all the findings. 



Some mixed studies reviews that used a parallel-results convergent synthesis design: