A systematic review is a summary of literature that uses explicit methods to perform a comprehensive literature search and critical appraisal of individual studies and that uses appropriate statistical techniques to combine these valid studies. (CEBM).
Key characteristics of a systematic review are:
Meta analysis is a systematic review that uses quantitative methods to synthesize and summarize the results.
Searching is a critical part of conducting the systematic review, as errors in the search process potentially result in a biased or otherwise incomplete evidence base. Searches for systematic reviews need to be constructed to maximise recall and deal effectively with a number of potentially biasing factors. (McGowan, 2005, p. 75)
You should aim to be as extensive as possible when conducting searches for systematic reviews. However, it may be necessary to strike a balance between the sensitivity and precision of your search.
Sensitivity – the number of relevant results identified divided by the total number of relevant results in existence
Precision - the number of relevant results identified divided by the total number of results identified.
Increasing the comprehensiveness of a search will reduce its precision and will retrieve more non-relevant results.
However,
... at a conservatively-estimated reading rate of two abstracts per minute, the results of a database search can be ‘scanread’ at the rate of 120 per hour (or approximately 1000 over an 8-hour period), so the high yield and low precision associated with systematic review searching is not as daunting as it might at first appear in comparison with the total time to be invested in the review. (Cochrane Handbook for Systematic Reviews of Interventions, 2011, Chapter 6.4.4)
A useful technqiue is to check the search strategies used in other systematic reviews for hints on terms and combinations to use. Several groups have also developed pre-tested search filters.
Highly recommended chapter: Booth, A., Papaioannou, D., & Sutton, A. (2012). Ch. 5: Searching the literature IN Systematic approaches to a successful literature review (pp. 71-96). London: SAGE Publications.
Types of reporting bias include:
For details see: Cochrane Handbook for Systematic Reviews of Interventions (2008, Chapter 10)
The following sites include examples of pre-tested search filters:
Centre for Evidence-Based Medicine - Formulating Answerable Clinical Questions
CIAP NSW Clinical Learning Module Asking a Clinical Question
Reproduced from: Bettany-Saltikov, J. (2010). Learning how to undertake a systematic review: Part 1. Nursing Standard, 24(40): p. 47-55.
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Systematic Review |
Literature Review |
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Question |
Focused on a single question |
Not necessarily focused on a single question, but may describe an overview |
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Protocol |
A peer review protocol or plan is included |
No protocol is included |
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Background |
Both provide summaries of the available literature on a topic |
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Objectives |
Clear objectives are identified |
Objectives may or may not be identified |
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Inclusion and Exclusion Criteria |
Criteria stated before the review is conducted |
Criteria not specified |
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Search Strategy |
Comprehensive search conducted in a systematic way |
Strategy not explicitly stated |
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Process of Selecting Articles |
Usually clear and explicit |
Not described in a literature review |
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Process of Evaluating Articles |
Comprehensive evaluation of study quality |
Evaluation of study quality may or may not be included |
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Process of Extracting Relevant Information |
Usually clear and specific |
Not clear or explicit |
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Results and Data Synthesis |
Clear summaries of studies based on high quality evidence |
Summary based on studies where the quality of the articles may not be specified. May also be influenced by the reviewer's theories, needs and beliefs |
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Discussion |
Written by an expert or group of experts with a detailed and well grounded knowledge of the issues |
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