Reviews of Evidence Flashcards
What is a systematic review?
An overview of primary studies that used explicit and reproducible methods
What are 3 main features of systematic reviews?
Transparent
Explicit
Reproducible
What is a meta-analysis?
Quantitative synthesis of the results of two or more primary studies that addressed the same hypothesis the same way.
(pools results)
What is the purpose of meta-analysis?
Quantify effect sizes and their uncertainty - used for risk-benefit analysis.
Collate results
How is study weighting decided in meta-analysis?
Size and uncertainty of OR (confidence interval)
If smaller CI then larger weight.
How are meta-analyses displayed?
Forest plot
What are problems with meta-analysis?
Heterogeneity between studies
Variable quality of studies
Publication bias in selection
How can heterogeneity between studies be adjusted for?
Fixed effects or random effects model
Analysis of variation - subgroup analysis.
What is fixed effects model?
Assumes studies are estimating exactly the same true effect size. All variation due to random error.
What is the random effects model?
Assumes studies are estimating similar, but not the same true effect size.
- Accounts for heterogeneity
What are the characteristics of random effects model?
Wider CI
More equal weighting - greater weighting for smaller studies.
What is the point of sub-group analysis?
Explain heterogeneity - random effects model accounts for variation but does not explain.
Why is there variability in study quality?
Poor study design
Poor design protocol
Poor protocol implementation (hard to assess)
Some studies prone to bias and confounding - case-control, cohort.
How can quality be maintained?
Define quality standard and only include studies fitting criteria. E.g. cochrane only RCTs
What is publication bias?
Studies with statistically significant or ‘favourable’ results are more likely to be published than those with non-statistically significant results.
