A systematic review attempts to collate all empirical evidence that fits pre-specified eligibility criteria in order to answer a specific research question. It uses explicit, systematic methods that are selected with a view to minimizing bias, thus providing more reliable findings from which conclusions can be drawn and decisions made.
The key characteristics of a systematic review are:
Meta-analysis is the use of statistical methods to summarize the results of independent studies. Many systematic reviews contain meta-analyses. By combining information from all relevant studies, meta-analyses can provide more precise estimates of the effects of health care than those derived from the individual studies included within a review. They also facilitate investigations of the consistency of evidence across studies, and the exploration of differences across studies.
Cochrane Handbook for Systematic Reviews of Interventions. Version 5.1.0. Updated March 2011. Section 1.2.2.
| Systematic review | Meta-Analysis | Topic/Literature review | |
|
Review question |
Starts with clear question to be answered or hypothesis to be tested |
Starts with clear question to be answered or hypothesis to be tested |
May also start with clear question to be answered, but more often involve general discussion of subject with no stated hypothesis |
|
Background |
Provide summaries of the available literature on a topic |
|
|
|
Searching for relevant studies |
Strive to locate all relevant published and unpublished studies to limit impact of publication and other biases |
Strive to locate all relevant published and unpublished studies to limit impact of publication and other biases May use funnel plot to assess completeness |
Do not usually attempt to locate all relevant literature. Strategy not explicitly stated |
|
Deciding which studies to include and exclude |
Involve explicit description of what types of studies are to be included to limit selection bias |
Involve explicit description of what types of studies are to be included to limit selection bias on behalf of reviewer |
Usually do not describe why certain studies are included and others excluded |
|
Assessing study quality |
Examine in systematic manner methods used in primary studies, and investigate potential biases in those studies and sources of heterogeneity between study results |
Quantitative analysis of measures of effect, accounting for heterogeneity |
Often do not consider differences in study methods or study quality |
|
Results and data synthesis |
Base their conclusions on those studies which are most methodologically sound |
Base their conclusions on those studies which are most methodologically sound |
Often do not differentiate between methodologically sound and unsound studies. May also be influenced by the reviewer's theories, needs and beliefs |
| Discussion | Written by an expert or group of experts with a detailed and well-grounded knowledge of the issues | Written by an expert or group of experts with a detailed and well-grounded knowledge of the issues |
Adapted from:
Petticrew M. Systematic reviews from astronomy to zoology: myths and misconceptions. BMJ. 2001 Jan 13;322(7278):98-101.
Bettany-Saltikov, J. (2010). Learning how to undertake a systematic review: Part 1. Nursing Standard, 24(40): 47-55.
Grant MJ, Booth A. A typology of reviews: an analysis of 14 review types and associated methodologies. Health Info Libr J. 2009 Jun;26(2):91-108.
Cochrane Handbook for Systematic Reviews of Interventions. Version 5.1.0. Updated March 2011. Section 1.2.2.
|
Systematic Review |
Meta-analyses | Narative Review | |
|
Strengths |
Reduces reviewer bias by use of objective, reproducible criteria to select relevant individual publications and assess their validity Saves decision-makers time |
Aggregates effects from several studies Small or inconclusive studies lacking in statistical significance can make a contribution to the larger picture Saves decision-makers time |
Generally comprehensive and cover a wide range of issues within a given topic Review articles can be used to bring one up-to-date on a particular topic |
|
Weakness |
Difficult and time consuming particularly when identifying appropriate studies Narrow focus and prescribed methods do not allow for comprehensive coverage |
Difficult and time consuming particularly when identifying appropriate studies Cannot eliminate (without registration of all trials) publication bias wherein positive findings get published and negative ones do not |
Subjective (terms of what studies to include) Selection bias (in terms of what studies to include) |
Adapted from:
Petticrew M. Systematic reviews from astronomy to zoology: myths and misconceptions. BMJ. 2001 Jan 13;322(7278):98-101.
Bettany-Saltikov, J. (2010). Learning how to undertake a systematic review: Part 1. Nursing Standard, 24(40): 47-55.
Grant MJ, Booth A. A typology of reviews: an analysis of 14 review types and associated methodologies. Health Info Libr J. 2009 Jun;26(2):91-108.
Cochrane Handbook for Systematic Reviews of Interventions. Version 5.1.0. Updated March 2011. Section 1.2.2.