Systematic review and meta-analysis

Question 1

What is a systematic review?

Answer 1

aims to answer defined research question by collecting and summarising empirical evidence that fits specific eligibility criteria from more than one study

Question 2

What is a meta analysis?

Answer 2

refers to statistical techniques used in a systematic review to integrate the results of studies

combines the estimates of effect from each study to ESTIMATE POOLED RISK

• allows more subjects to be included so effect estimated more reliable and precise
• difference (heterogeneity) identified and explored and if too great, cannot pool results

Question 3

Why do a systematic review?

Answer 3

• data quantity (increase number of studies/paper over years)
• data quality
• individual studies not powerful enough to answer research question so SR allows generalisable conclusions to be made through summarising knowledge around research question
• many studies of same question yield inconsistent/opposing results

Question 4

How to assess quantity and quality of data?

Answer 4

efficient searching of data (literature)

apply formal rules for critical appraisal of data sources

Question 5

Advantages of systematic approach?

Answer 5

• transparent method as methods to identify and reject studies are explicit
• meta analysis can be used to improve power by enhancing precision of estimates of treatment effects, account for sample size, uncertainties

Question 6

Stage I systematic review?

Answer 6

planning review

- define research question

Question 7

Stage II systematic review?

Answer 7

identify research 
select studies 
- define inclusion/exclusion criteria
study quality assessment 
- assess bias 
- against specific criteria

Question 8

Stage III of systematic review?

Answer 8

report and dissemination
- collect study details for eligible studies on sample size, interventions/exposure, population details, summary of findings

Question 9

Last stage of systematic review?

Answer 9

estimate overall effect by combining data, if meta analysis is appropriate

Question 10

Advantages of meta-analysis?

Answer 10

• generate pooled risk estimate
• more reliable/precise estimate of effect
• explore heterogeneity between published studies
• identify if publication bias present

Question 11

Disadvantage of meta-analysis?

Answer 11

• publication bias
• labour intensive
• inconsistent results due to difference in studies
• low study quality

Question 12

What is the most common way of visually summarising results of meta analysis ?

Answer 12

Forest plot

shows results from studies and meta-analysis results

Question 13

How is statistics of systematic review done?

Answer 13

studies in SR generate individual effect estimates

meta-analysis pools these estimates to generate weighted average effect across all studies

Question 14

What is publication bias?

Answer 14

greater likelihood of research with statistically significant results to be published in peer reviewed literature

may not include all data in meta-analysis leading to effect of exposure/intervention being over or under estimated

Question 15

How is publication bias explored?

Answer 15

Funnel plots

show whether there is a link between study size (precision) and effect estimate

Question 16

What is heterogeneity and how is it explored?

Answer 16

studies that answer same question may still differ by design

explored using Galbraith (radial) plots

but if too much heterogeneity, not appropriate to pool studies

Question 17

Limitations in systematic review?

Answer 17

• if few studies that match eligibility criteria, SR may not add much to review
• methodological quality of study may be poor
• publication bias can distort findings as stat significant findings more likely to get published

Question 18

Critically appraise SR?

Answer 18

1. clear, predefined question?
2. comprehensive search for literature?
3. methodological quality of studies assessed?
4. heterogeneity explored?
5. evidence credible?
6. check guidelines for reporting PRISMA?

Question 19

Critically appraise MA?

Answer 19

1. heterogeneity explored?
2. publication bias an issue?
3. was it appropriate to pool studies?
4. appropriate model used to pool effect estimates?
5. did different sub groups of studies give similar results?

Question 20

What 3 things do MA do?

Answer 20

• better estimate of intervention/exposure effect
• understand similarities/difference between studies
• assess publication bias

Question 21

What do SR/MA do ?

Answer 21

provide evidence base for clinical decisions