It is a structured review integrating pooling the results ( Meta-analysis ) of individual studies addressing the same topic.
structured : for consistent presentation of information
Meta-Analysis : combine and statistically summarize the results of individual studies
Cook, D. J. et. al. Ann Intern Med 1997;126:376-380 Differences between Narrative Reviews and Systematic Reviews
QUESTION Broad Focused SOURCES/ Usually unspecified Comprehensive; SEARCH Possibly biased explicit SELECTION Unspecified; biased?Criterion-based; uniformly applied APPRAISAL Variable Rigourous SYNTHESIS Usually qualitative Quantitative INFERENCE Sometimes Usually evidence- evidence-based based NARRATIVE SYSTEMATIC Cook, D. J. et. al. Ann Intern Med 1997;126:376-380
Level of evidence
I–1 Systematic reviews.
I–2 One or more large double-blind randomised control trials.
II–1 One or more well-conducted cohort studies.
II–2 One or more well-conducted case-control studies.
II–3 uncontrolled experiment.
III Expert opinion.
IV Personal experience
Why on the Top
Relatively large sample size
Ensures the highest quality evidence
Why do we need it
Too much trials
25000 biomedical journals in print
8000 articles published per day
All studies not equally well designed or interpreted
So , we need a study of studies
To summarize evidence from studies that address a specific clinical question.
to explain differences among studies on the same question
In a way that limit bias (rigorous methodology & clear reporting)
Protocols in neurology units - 80% still recommend bed rest after LP
Systematic review of 10 trials of bed rest after spinal puncture
no change in headache with bed rest
Increase in back pain
Serpell M, BMJ 1998;316:1709–10
Why do we need it
many single trials had relatively low power
avoid Type II error: Investigators did not detect a difference when a difference actually exists
This is not surprising as the power to detect a difference will have been increased by the increase in the sample size
Graphic Display: ß blockers in secondary prevention after myocardial infarction .
Why do we need it
Systematic reviews help us to avoid the personal bias inherent in traditional reviews and expert opinion
Why do we need it Example
Mitchell JRA. Timolol after myocardial infarction: an answer or a new set of questions? BMJ 1981 ; 282:1565-70 :
"despite claims that they reduce arrhythmias, cardiac work, and infarct size, we still have no clear evidence that ß blockers improve long-term survival after infarction despite almost 20 years of clinical trials."
Why do we need it
Results from systematic reviews are the cornerstone for developing practice guidelines
The current resource with the highest methodological rigor
$235/year or abstracts only
Specific point: e.g role of albumin in OHSS
Abstract Background Objectives Criteria for considering studies for this review Types of participants Types of intervention Types of outcome measures Types of studies Search strategy for identification of studies Methods of the review Description of the studies Methodological qualities of included studies Results Discussion Conclusions Implications for practice Implications for research Internal sources of support to the review External sources of support to the review Potential conflict of interest Acknowledgements Contribution of Reviewer(s) Synopsis Characteristics of included studies Table 01 results References to studies included in this review Additional references Typical Systematic Review “Skeleton”
Steps to do
Efficient Search Strategies
Review Abstracts to Determine Eligibility
Apply Strict Inclusion/Exclusion Criteria
Extract the Data
Perform the Required Analyses (Meta-analysis)
Interpret the Results
Determine Implications for Health Care Policy and Practice
At least 3 reviewers
7 peer reviewers
Trial design characteristics
Why included / excluded
Quality of included studies in details
Some Controversies About Meta-Analysis
Quality of Studies
Many Small Studies or One Big Study?
Try to make it prospective
the first prospective systematic review in the entire field of gynecology . (Al-Inany & Aboulghar)
Repeat the analysis
Excluding the unpublished studies (if there were any)
Excluding studies of the lowest quality
If there were one or more very large studies, the analysis would be repeated excluding them to look at how much they dominate the results.
Meta-analysis vs. a “Mega-study”
Single large studies are liable to:
a drug that reduces mortality by 10% from myocardial infarction may need a study including 10.000 patient
Generalizability of results can be questioned .
Human Albumin Model
The objective was to review the effectiveness of human albumin administration in prevention of severe ovarian hyperstimulation syndrome
The MDSG specialised register
Abstracts from conferences
handsearching of core journals
contact with authors of relevant papers.
Only randomised controlled studies
2.2% in albumin group / 7.7% in control group
absolute risk reduction was 5.5%
NNT = 1/ARR
For every 18 women at risk of severe OHSS, albumin infusion will save one more case.
Whether this NNT would justify the routine use of albumin infusion in cases at risk of severe OHSS needs to be judged by clinical decision makers.
Keep in mind Evidence may change with more trials
challenges for systematic reviews
Evidence into practice
Many interventions reviewed cannot be implemented in resource-poor situations
Most interventions reviewed so far don’t reflect developing world priorities
very few studies that have been conducted in a developing country
Most developing country research that is found is excluded on quality grounds
Problems in Contribution
Lack of EBM awareness
Lack of training workshops
Lack of Financial resources
Lack of access to information
“ Applied for grant but was refused on basis of this not being research in real sense and just a review of literature ”
Systematic reviews are now recognized as a 2ry research
Hence, the Cochrane collaboration changed the name of the contributor from reviewer to author
Address priority topics
it is vital to invest in health care that works (for limited resources)
Disseminating the findings of systematic reviews to policymakers