Posted on February 3, 2016
Tags: evidence based decisions, review, Systematic reviews
Millions of articles are published yearly(1), making it difficult for clinicians to keep abreast of the literature. Reviews of literature are necessary in order to provide clinicians with accurate, up to date information to ensure appropriate management of their patients. Reviews usually involve summaries and synthesis of primary research findings on a particular topic of interest and can be grouped into 2 main categories; the ‘traditional’ review and the ‘systematic’ review with major differences between them.
Traditional reviews provide a broad overview of a research topic with no clear methodological approach(2). Information is collected and interpreted unsystematically with subjective summaries of findings. Authors aim to describe and discuss the literature from a contextual or theoretical point of view. Although the reviews may be conducted by topic experts, due to preconceived ideas or conclusions, they could be subject to bias.
Systematic reviews are overviews of the literature undertaken by identifying, critically appraising and synthesising results of primary research studies using an explicit, methodological approach(3). They aim to summarise the best available evidence on a particular research topic.
The main differences between traditional reviews and systematic reviews are summarised below in terms of the following characteristics: Authors, Study protocol, Research question, Search strategy, Sources of literature, Selection criteria, Critical appraisal, Synthesis, Conclusions, Reproducibility, and Update.
- Authors: One or more authors usually experts in the topic of interest
- Study protocol: No study protocol
- Research question: Broad to specific question, hypothesis not stated
- Search strategy: No detailed search strategy, search is probably conducted using keywords
- Sources of literature: Not usually stated and non-exhaustive, usually well-known articles. Prone to publication bias
- Selection criteria: No specific selection criteria, usually subjective. Prone to selection bias
- Critical appraisal: Variable evaluation of study quality or method
- Synthesis: Often qualitative synthesis of evidence
- Conclusions: Sometimes evidence based but can be influenced by author’s personal belief
- Reproducibility: Findings cannot be reproduced independently as conclusions may be subjective
- Update: Cannot be continuously updated
- Authors: Two or more authors are involved in good quality systematic reviews, may comprise experts in the different stages of the review
- Study protocol: Written study protocol which includes details of the methods to be used
- Research question: Specific question which may have all or some of PICO components (Population, Intervention, Comparator, and Outcome). Hypothesis is stated
- Search strategy: Detailed and comprehensive search strategy is developed
- Sources of literature: List of databases, websites and other sources of included studies are listed. Both published and unpublished literature are considered
- Selection criteria: Specific inclusion and exclusion criteria
- Critical appraisal: Rigorous appraisal of study quality
- Synthesis: Narrative, quantitative or qualitative synthesis
- Conclusions: Conclusions drawn are evidence based
- Reproducibility: Accurate documentation of method means results can be reproduced
- Update: Systematic reviews can be periodically updated to include new evidence
Decisions and health policies about patient care should be evidence based in order to provide the best treatment for patients. Systematic reviews provide a means of systematically identifying and synthesising the evidence, making it easier for policy makers and practitioners to assess such relevant information and hopefully improve patient outcomes.
- Fletcher RH, Fletcher SW. Evidence-Based Approach to the Medical Literature. Journal of General Internal Medicine. 1997; 12(Suppl 2):S5-S14. doi:10.1046/j.1525-1497.12.s2.1.x. Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1497222/
- Rother ET. Systematic literature review X narrative review. Acta paul. enferm. [Internet]. 2007 June [cited 2015 Dec 25]; 20(2): v-vi. Available from: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-21002007000200001&lng=en. http://dx.doi.org/10.1590/S0103-21002007000200001
- Khan KS, Ter Riet G, Glanville J, Sowden AJ, Kleijnen J. Undertaking systematic reviews of research on effectiveness: CRD’s guidance for carrying out or commissioning reviews. NHS Centre for Reviews and Dissemination; 2001.