Synthesising and interpreting evidence

 

What is meant by “synthesis”?

Synthesis is not simply describing each study in turn.  In fact, synthesis involves looking for patterns, spotting similarities and differences between studies or findings.  Pope, Mays & Popay state that synthesis seeks to demonstrate that "the whole is greater than the sum of its parts" i.e. that the synthesis activity adds some value (1).

 

Understanding and communicating risk and uncertainty

When producing a digest or evidence briefing, the interpreting of evidence is about communication and understanding – the skill lies in using familiar language to explain the less familiar and more complicated.

Cognitive bias may interfere with our perceptions of risk and likelihood.  For instance if something happened recently, or had a serious consequence, we may estimate that it happens more regularly than it actually does. 

In technical (i.e. statistical) terms, “significant” means that something is unlikely to have occurred by chance, so it refers to a likelihood greater than 1 in 20.  More information can be found in our Statistics page.

 

Generalisability and making recommendations

It can be challenging to take results from a particular population (ie. the study population) and apply them to your own population:  

• internal validity (ie. “how good is the study?”)
• external validity or generalisability (ie. “how do the study results apply to my population?).

When writing a summary or evidence brief, it may be helpful to keep a checklist to remind you of the issues that could make an intervention more or less effective in your own practice compared with the research study. 

 

References:

(1) Pope, C, Mays, N, Popay, J, 2007. Synthesizing qualitative and quantitative health evidence: a guide to methods. Open University Press.

 

Adapted from training entitled Instant evidence based medicine: how to quickly synthesise research, delivered by School of Health and Related Research, University of Sheffield on 6th September 2018, Glasgow.