Systematic Reviews, Meta-Analysis And Heterogeneity Flashcards
What are the key aspects of a systematic review?
- EXPLICIT statements are made in regards to study design and outcomes
- TRANSPARENT methodology
- REPRODUCIBLE by anyone
Define ‘systematic review’
An overview of primary studies that uses explicit, transparent and reproducible methods
Define ‘meta analysis’
A quantitative synthesis of the results of two or more primary studies that addressed the same hypothesis in the same way
What is the purpose of a meta analysis?
- Quantify effect sizes (OR and 95% CI) of a large number of studies as a POOLED ESTIMATE
- Systematically collate and facilitate the synthesis of a large number of study results
- Reduce problems in interpretation due to variations in sampling
What model is used to display a meta analysis?
Forest plot
Explain how a pooled estimate is calculated in a meta analysis
- Odds ratio and 95% CI calculated for each study in meta analysis
- Combined to give a pooled OR and 95% CI using statistical computer
- Studies are WEIGHTED according to their size and uncertainty in OR (error factor)
What is the effect of error factor on the weighting of studies in a meta analysis?
Smaller error factor means LARGER WEIGHTING GIVEN
Describe what the following mean in a forest plot: 1 - square 2 - dotted line 3 - diamond 4 - solid line
1 - shows each individual odds ratio with their 95% CI (larger square means greater weighting is given)
2 - pooled odds ratio for all studies
3 - pooled 95% CI (points on diamond represent lower and upper limits)
4 - null value
What is heterogeneity?
- % measure of how similar the studies in the meta analysis are
- Assesses whether the difference in the individual trials was due to random variation (within studies)
How could you tell if the differences between studies in a meta analysis was due to random variation with the studies themselves?
- If p
How could you model for variation between study designs in a meta analysis?
- Fixed effect model vs Random effects model
- Often a WEAK test for heterogeneity
What is the difference between a fixed effect model and a random effects model?
- Fixed effect model assumes studies are ESTIMATING THE EXACT SAME EFFECT SIZE
- Random effects model assumes the studies are ESTIMATING SIMILAR, BUT NOT THE SAME EFFECT SIZE
How does the weighting of studies differ in a random effects model compared to a fixed effect model?
- Weighting is MORE EQUAL
- However there is a WIDER 95% CI
Describe a way in which you could test for heterogeneity without using a fixed/random effects model approach
- SUB GROUP ANALYSIS
- Stratification of studies by study characteristics and participant profile
Describe how the quality of studies can vary
- Some studies are more prone to confounding and bias
- Poor study design and protocol
- Poor protocol implementation
What is publication bias?
- Publication of studies that show favourable and statistically significant results
- Leads to a biased selection of studies towards demonstration of effect
What model could you use to measure the publication bias of a systematic review?
- FUNNEL PLOT
- If plot resembles a funnel shape there is less/no publication bias
How could you decrease publication bias?
- Include smaller studies
- Include unpublished studies
- Include studies in different languages
How could you approach the variable quality of studies in a systematic review?
- Only include studies above a certain quality standard
- Assess the impact of quality in the pooled effect size
What is meant by ‘evidence based medicine’?
Healthcare services and interventions should be based on the best available evidence, which results from rigorously conducted research
