Synthesising and summarising evidence

Find out how to synthesise and summarise the evidence for users.

Overview

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.

Searches

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.

Summarising and synthesising

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 2 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)

Examples 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.

Resources