New insights from completed studies

Secondary research uses information that has already been compiled and formatted. [1]

One common form of secondary research drawing on existing research is a summary and/or synthesis of studies completed by others. It is a ‘study of studies’ often across contexts and/or populations.

Rigorous reviews of the evidence help everyone to make informed decisions about care. Evidence synthesis refers to methods used to bring together the findings of completed research to summarise what is known from that research on a specific topic.

Reviews help clinicians by:

  • Providing a clear summary of the best research evidence and what is known
  • Highlighting best practice and hence guiding decision-making
  • Avoiding ineffective or harmful practices
Palliative care professionals can make use of a range of open access resources that enable an examination of structured reviews from a range of disciplines and relevant to palliative care. These include guidelines and formal guidance from national and international bodies.

In health care, meta-analysis and systematic reviews are highly ranked because of the rigorous approach taken to searching for all relevant studies and the measures taken to account for bias. [2] While systematic reviews provide the most thorough examination of available evidence they require a lot of time and resources. In the policy context, timeliness matters and time limited formats such as rapid reviews or policy briefs are common. The following lists some of the review types.

Study design Definition


The use of statistical techniques in a systematic review to integrate the results of included studies. Sometimes used as a synonym for systematic reviews, where the review includes a meta-analysis. [3] The validity of a meta-analysis depends on the quality of studies included in the systematic review. View an example - Implementation and Effectiveness of Integrating Palliative Care Into Ambulatory Care of Noncancer Serious Chronic Illness: Mixed Methods Review and Meta-Analysis.

Systematic review

Summaries of research evidence that address a clearly formulated question using systematic and explicit methods to identify, select, and critically appraise relevant research, and to collect and analyse data from the studies that are included in the review. [3] View an example - Pediatric palliative care and end-of-life: a systematic review of economic health analyses.

Rapid review

A form of knowledge synthesis that accelerates the process of conducting a traditional systematic review through streamlining or omitting specific methods to produce evidence for stakeholders in a resource-efficient manner. [4] View an example - A rapid review of end-of-life needs in the LGBTQ+ community and recommendations for clinicians.

Realist review

A theory-based method for synthesis of findings from a number of qualitative studies.. [3] View an example - A realist review of advance care planning for people with multiple sclerosis and their families.

Narrative review

A summary in words (rather than numerically) of, for example, the effects of a policy or program option. Narrative reviews are not always based on a thorough and reproducible search of the literature for studies that address the review question. [3] View an example - Palliative Sedation-The Last Resort in Case of Difficult Symptom Control: A Narrative Review and Experiences from Palliative Care in Switzerland.

Scoping review

A form of knowledge synthesis that addresses an exploratory research question aimed at mapping key concepts, types of evidence, and gaps in research related to a defined area or field by systematically searching, selecting, and synthesizing existing knowledge. [5] View an example - Advance Care Planning in Neurodegenerative Disorders: A Scoping Review.

Umbrella review

A review of other systematic reviews on a topic. This takes into consideration the quality of completed systematic reviews and comparison of any conclusions drawn. View an example - Advance care planning for people living with dementia: An umbrella review of effectiveness and experiences.

Preparing a review

If you want to prepare your own review of evidence there are some tasks common across the different formats that you will need to consider, these are listed below. [6] If you are looking for more on how to prepare a review visit University of South Australia's modules on Systematic reviews and Scoping reviews. For guidance on preparing policy syntheses you could read the BMJ SUPPORT Tools series of articles.

Steps in review synthesis

  • Stating the objectives of the research
  • Defining eligibility criteria for studies to be included;
  • Identifying (all) potentially eligible studies (and keeping track of what has been found);
  • Applying eligibility criteria;
  • Assembling the most complete data set feasible, including,
    • data extraction;
    • quality appraisal of included studies;
  • Analysing this data set, using statistical synthesis and sensitivity analyses if appropriate and possible for quantitative studies; approaches suggested for qualitative studies include thematic synthesis, framework synthesis, grounded theory, meta-narrative, or meta-ethnography. [7,8]
  • Preparing a structured report of the research.
  • Addressing whether the evidence supports the need for change or not

  1. Oxford Reference. Secondary research [Internet]. Oxford: Oxford University Press; Oxford: 2022. [cited 2022 May 15].
  2. Vere J, Gibson B. Variation amongst hierarchies of evidence. J Eval Clin Pract. 2021 Jun;27(3):624-630. doi: 10.1111/jep.13404. Epub 2020 May 4.
  3. Cochrane. Glossary [Internet]. London: Cochrane; 2011. [updated 2011 Nov; cited 2022 May 9].
  4. Garritty C, Gartlehner G, Kamel C, King VJ, Nussbaumer-Streit B, Stevens A, et al. Cochrane Rapid Reviews. Interim Guidance from the Cochrane Rapid Reviews Methods Group (192kb pdf). London: Cochrane; 2020 Mar.
  5. Colquhoun HL, Levac D, O'Brien KK, Straus S, Tricco AC, Perrier L, et al. Scoping reviews: time for clarity in definition, methods, and reporting. J Clin Epidemiol. 2014 Dec;67(12):1291-4. doi: 10.1016/j.jclinepi.2014.03.013. Epub 2014 Jul 14.
  6. Grimshaw J. A Guide to Knowledge Synthesis [Internet]. Ottawa, ON: Canadian Institutes of Health Research; 2010. [updated 2010 Apr 8; cited 2022 May 11].
  7. Noyes J, Booth A, Cargo M, Flemming K, Harden A, Harris J, et al. Chapter 21: Qualitative evidence. In: Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA, editors. Cochrane Handbook for Systematic Reviews of Interventions. version 6.3. London: Cochrane; 2022.
  8. Barnett-Page E, Thomas J. Methods for the synthesis of qualitative research: a critical review. BMC Med Res Methodol. 2009 Aug 11;9:59. doi: 10.1186/1471-2288-9-59.

Page created 13 April 2022