Transcript Studies included in a Systematic Review

http://bahrain.cochrane.org/en/index.html
http://www.rt.ae
The Bahrain Branch of the UK Cochrane Centre
In Collaboration with
Reyada Training & Management Consultancy, Dubai-UAE
Cochrane Collaboration and Systematic
Review Workshop, 20-21 February 2007,
Dubai - UAE
W12
Dr. Zbys Fedorowicz, Dr. Dunia Al Hashimi, Dr. Ahmed Al Asfoor
Methodological quality of
studies to be included in a
Systematic Review
Study quality
Quality: a multidimensional concept:
related to the
1. Design
2. Conduct
3. Analysis of a trial
4. Quality of reporting
Internal Validity
AND/OR
Its clinical relevance i.e. External Validity
The validity of findings in a
study
Internal extent to which systematic error
(bias) is minimised in clinical trials
[Selection/Performance/Detection/Attrition]
External extent to which results provide a
correct basis for generalisation to other
circumstances (i.e. clinical applicability)
Assessment of study quality
Quality scales vs checklist
Validity assessment can be used:
- as a threshold for inclusion of studies
- as a possible explanation for heterogeneity
- in sensitivity analyses
- as weights in meta-analysis
Quality scales
• Jadad scale : Bias in Pain Research
Reports: Scaled< 5
What’s missing?
Check lists
Cochrane “Risk of Bias” Tables
• Randomisation
• Allocation Concealment
• Blinding of Outcomes Assessment
• Attrition
Everything covered?
Limitations of quality assessment
* Inadequate reporting of trials
* Lack of empirical evidence
* Subjectivity
Meta-analysis
* Statistical combination of results, estimating
the weighted average of treatment effect.
* Investigating heterogeneity across studies:
subgroup analysis
meta-regression
Heterogeneity?
(variations/differences)
Variation in results across studies
Statistical heterogeneity
Clinical
heterogeneity
Methodological
heterogeneity
Clinical heterogeneity
might arise from differences between:
• Participants (e.g. sex, age, severity of
illness)
• Interventions being compared
• Outcomes collected.
Methodological heterogeneity
arises through the use of:
• different trial designs (e.g. parallel,
cross-over trials, cluster-randomised
trials) and
• different degrees of control over bias
(e.g. risk may differ depending on
allocation concealment, blinding, loss to
follow up).
Statistical heterogeneity
a consequence of clinical
AND
methodological heterogeneity
Sources of heterogeneity
Chance
Variations in patients
Variations in interventions
Different outcome measures
Methodological quality
Dealing with heterogeneity
Assessing homogeneity:
-
Graphical methods
statistical testing
Investigating heterogeneity:
-
subgroup analysis
meta-regression
Clinical heterogeneity
Homogeneous trials:
studies have similar interventions received by
similar participants.
Statistical testing for homogeneity
Chi Squared / I2 statistic
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