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The Bahrain Branch of the UK Cochrane Centre In Collaboration with Reyada Training & Management Consultancy, Dubai-UAE Cochrane Collaboration and Systematic.

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Presentation on theme: "The Bahrain Branch of the UK Cochrane Centre In Collaboration with Reyada Training & Management Consultancy, Dubai-UAE Cochrane Collaboration and Systematic."— Presentation transcript:

1 The Bahrain Branch of the UK Cochrane Centre In Collaboration with Reyada Training & Management Consultancy, Dubai-UAE Cochrane Collaboration and Systematic Review Workshop, February 2007, Dubai - UAE Dr. Zbys Fedorowicz, Dr. Dunia Al Hashimi, Dr. Ahmed Al Asfoor W12

2 Methodological quality of studies to be included in a Systematic Review

3 Study quality Quality: a multidimensional concept: related to the 1.Design 2.Conduct Internal Validity 3.Analysis of a trial 4.Quality of reporting AND/OR Its clinical relevance i.e. External Validity

4 The validity of findings in a study External extent to which results provide a correct basis for generalisation to other circumstances (i.e. clinical applicability) Internal extent to which systematic error (bias) is minimised in clinical trials [Selection/Performance/Detection/Attrition]

5 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

6 Quality scales Jadad scale : Bias in Pain Research Reports: Scaled< 5 What’s missing?

7 Check lists Cochrane “Risk of Bias” Tables Randomisation Allocation Concealment Blinding of Outcomes Assessment Attrition Everything covered?

8 Limitations of quality assessment * Inadequate reporting of trials * Lack of empirical evidence * Subjectivity

9 Meta-analysis * Statistical combination of results, estimating the weighted average of treatment effect. * Investigating heterogeneity across studies: subgroup analysis meta-regression

10 Variation in results across studies Heterogeneity? (variations/differences) Statistical heterogeneity Clinical heterogeneity Methodological heterogeneity

11 Clinical heterogeneity might arise from differences between: Participants (e.g. sex, age, severity of illness) Interventions being compared Outcomes collected.

12 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). Methodological heterogeneity

13 Statistical heterogeneity a consequence of clinical AND methodological heterogeneity

14 Chance Variations in patients Variations in interventions Different outcome measures Methodological quality Sources of heterogeneity

15 Dealing with heterogeneity Assessing homogeneity: -Graphical methods -statistical testing Investigating heterogeneity: -subgroup analysis -meta-regression

16 Clinical heterogeneity Homogeneous trials: studies have similar interventions received by similar participants.

17 Chi Squared / I 2 statistic Statistical testing for homogeneity

18 INFORMATION OVERLOAD


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