S7: evidence based medicine

Question 1

Outline the hierarchy of evidence

Answer 1

Strongest: meta-analyses & systematic reviews, RCTs, cohort studies
Weakest: case reports, opinion letters & letters, animal trials & in vitro studies, cross sectional studies

Question 2

Define a systematic review

Answer 2

A summary of medical literature on a topic, conducted using explicit methods
Very credible source of evidence – explicit, transparent and reproducible

Question 3

Define a meta-analysis

Answer 3

A quantitative synthesis of the results of two or more primary studies that addressed the same hypothesis in the same way

Question 4

List problems of a meta-analysis

Answer 4

Heterogeneity between studies
Variable quality of the studies
Publication bias in selection of studies

Question 5

Describe publication bias

Answer 5

Studies with statistically significant or ‘favourable’ results are more likely to be published than those with non-statistically significant or ‘unfavourable’ results
Any systematic review or meta-analysis can be flawed by such bias