Synthesising and summarising evidence
About how to synthesise and summarise the evidence for users.
Overview of the topic
The Knowledge for Healthcare Framework (2021) identifies the growing demand for knowledge and library staff to search and present evidence that is synthesised and summarised.
Lots of terminology is used interchangeably to describe the products we create and share with users. These include:
- literature search
- evidence search
- literature review
- evidence summary
- evidence synthesis
- evidence brief
- search with summary
- systematic review
The range of language used, the way they overlap, and the inconsistencies in how they are applied, can make understanding the differences between them all difficult.
A “search” is the strategic approach to finding and collating evidence, references, and results, relevant to the question posed by a user.
Often searchers scan databases containing studies relevant to their topic, for example MEDLINE, a general medical database.
Searches will often also involve scanning other resources on the internet to retrieve grey literature, case studies or reports. A definition of grey literature may be found at the National Grey Literature Collection.
The search process, and the collation of the results into a document, might be described as a literature search or evidence search, and would contain:
- a list of the references retrieved
- citation details
- an abstract briefly describing the findings of each result
A search often includes a description of the search strategy, resources searched, and potentially some short comments from the searcher.
When we talk about summarising or synthesising, we refer to the process of taking the list of results or references retrieved as part of a literature search and manipulating them to produce a more detailed report or document that is sent to users to help with their decision-making.
A “summary” might include:
- a description of the search strategy
- comments from the searcher on the search process or results
- brief descriptions of headlines from key results, or an indication of themes that have emerged
Booth describes an evidence summary as functioning “like an honest broker who neutrally gathers factual information to support the decision-making process.”
Summaries may or may not include a quality assessment of individual documents.
Summaries might range from a few sentences to a paragraph or two presented before the list of results.
A “synthesis” goes a step further. Analysis is undertaken across the result set, the findings from multiple studies are considered to identify themes, similarities, and differences, and they may or may not include quality assessment across multiple documents.
Synthesis is usually a key part of the process of a systemic review, a type of literature review where the best available evidence relating to a specific research question is located, appraised, and synthesised, and overall conclusions can be provided.
When producing a synthesis as part of a systematic review a quality assessment (also known as critical appraisal) of each individual study may be required using a checklist appropriate to the study design.
A list of checklists for critical appraisal can be found on the Critial Appraisal Skills Programme (CASP) website.
It is possible then for searchers to conduct a search and present:
- the results in a list (search)
- the results with additional commentary potentially highlighting key documents or themes, (summary)
- an analysis of the results in more detail providing a more considered discussion of the results as a whole (synthesis)
Example from practice
Below are some examples of different kinds of searches, summaries, and synthesis to convey the wide variety of ways the results of a search can be pulled together and evaluated.
Based on these definitions this example, Employee Reward and Recognition – Recent Research is of a summary, almost synthesis, whilst this one, Use of patient restraints in critical care or HDU/ICU is more of a brief summary/ search.
Resources
Blogs
Blog about rapid reviewing by Jon Brassey, who also runs the TRIP database.
Courses
GRADE Online Learning Modules (McMaster University)
Online learning modules to help guideline developers and authors of systematic reviews learn how to use the GRADE approach to grade the evidence in systematic reviews.
Sheffield University: SchARR (School of Health and Related Research)
Qualitative and quantitative synthesis. Fee paying bookable courses.
E-books
The Cochrane Library contains six databases that contain different types of high-quality evidence. The Cochrane handbook explains how Cochrane reviews are produced.
University of York CRD: Systematic Reviews
In-depth guidance on how to carry out a systematic review.
Journal articles
On three previous occasions, we have attempted to systematically search for and synthesise public health grey literature and information—both to summarise the extent and nature of particular classes of interventions and to synthesise results of evaluations.
Here, we briefly describe these three ‘case studies’ but focus on our post hoc critical reflections on searching for and synthesising grey literature and information garnered from our experiences of these case studies.
EVIDENT Guidance for Reviewing the evidence: a compendium of methodological literature and websites
Evidence Synthesis for Decision Making, Parts 1 -7. Medical Decision Making
A series of seven tutorial papers on evidence synthesis methods for decision making.
Websites
Evidence summaries process guide, NICE
PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analysis)
Evidence-based minimum set of items for reporting in systematic reviews and meta-analyses. Provides a checklist and flow diagram. This also helps to develop understanding of research design.
University of York Centre for Reviews and Dissemination (CRD)
CRD is a world renowned institute that produces policy relevant research and innovative methods that advance the use of research evidence to improve population health.