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Synthesize included studies

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Saved by Quan Nha HONG
on April 25, 2016 at 10:07:55 am

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 were presented at the CADTH Symposium 2016 (see poster)

Reference: Hong, Q.N., Pluye, P., Bujold, M., Wassef, M. 2016 Systematic mixed studies reviews: How qualitative and quantitative evidence are synthesized? CADTH Symposium, Ottawa, 10-12 avril 2015 (poster).



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: 

  • Mills EJ, Seely D, Rachlis B, Griffith L, Wu P, Wilson K, et al. (2006). Barriers to participation in clinical trials of cancer: a meta-analysis and systematic review of patient-reported factors. The Lancet Oncology, 7(2), 141-148.
  • Pluye P, Grad RM, Dunikowski LG, Stephenson R (2005). Impact of clinical information-retrieval technology on physicians: a literature review of quantitative, qualitative and mixed methods studies. International Journal of Medical Informatics, 74(9), 745-768.


2) Convergent synthesis designs


In the convergent synthesis design, results of included studies are complementary. We found that the integration can occur at 3 different levels: during the synthesis of data, 


A) Integration during the synthesis of the data

First, there is a qualitative synthesis of results of qualitative, quantitative, and mixed methods studies (QUAL). In the data extraction for a qualitative synthesis, results of qualitative, quantitative, and mixed methods studies are transformed into themes such as constructs, concepts and factors. It is called qualitization of the data. Examples of convergent designs with qualitative synthesis: thematic synthesis, realist review, critical interpretive synthesis, meta-narrative synthesis, and multiple case synthesis. 


Second, there is a quantitative synthesis of results of qualitative, quantitative and mixed methods studies (QUAN). In the data extraction for a quantitative synthesis, results of qualitative, quantitative, and mixed methods studies are transformed into variables and values. It is called quantization of the data. Examples of convergent designs with quantitative synthesis: 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 convergent qualitative synthesis: 

  • Bélanger E, Rodríguez C, Groleau D (2011). Shared decision-making in palliative care: a systematic mixed studies review using narrative synthesis. Palliative Medicine, 25(3), 242-261.
  • Lewis SA, Noyes J, Mackereth S, Lewis SA, Noyes J, Mackereth S (2010). Knowledge and information needs of young people with epilepsy and their parents: Mixed-method systematic review. BMC Pediatrics, 10, 103.
  • Buelens M, Woestyne M, Mestdagh S, Bouckenooghe D (2008). Methodological issues in negotiation research: A state-of-the-art-review. Group Decision and Negotiation, 17(4), 321-345.
  • Classen S, Lopez EDS (2006). Mixed methods approach explaining process of an older driver safety systematic literature review. Topics in Geriatric Rehabilitation, 22(2), 99-112.


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


Example adapted from Keating et al. (2011)


Phases Review question Output
Phase 1  Qualitative question: What are the views of COPD patients on the barriers and facilitators influencing the attendance to pulmonary rehabilitation?     Five major themes of barriers
Phase 2 Quantitative questions:  Is there any association between the level of up-take and completion of pulmonary rehabilitation by COPD patients and the identified barriers and facilitators? Odd ratio (association between factors identified in phase 1 and level of uptake and completion of the interventions)
Final integration    Impact of barriers and facilitators on uptake and completion of the intervention

Example adapted from Campbell et al. (2011)


Review question


Phase 1 

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

Phase 2

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

Final integration


Explanation of the success or failure of the intervention


  • Campbell F, Johnson M, Messina J, Guillaume L, Goyder E (2011). Behavioural interventions for weight management in pregnancy: A systematic review of quantitative and qualitative data. BMC Public Health, 11.
  • Harden A, Brunton G, Fletcher A, Oakley A (2009). Teenage pregnancy and social disadvantage: systematic review integrating controlled trials and qualitative studies. British Medical Journal, 339, b4254.
  • Thomas J, Harden A, Oakley A, Oliver S, Sutcliffe K, Rees R, et al. (2004). Integrating qualitative research with trials in systematic reviews. British Medical Journal, 328(7446), 1010-1012.


C) Integration during the discussion



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