11 and 12 POP SCI- need to do

Question 1

What is a systematic review? What is the purpose of a systematic review?

Answer 1

A systematic review is an overview of primary studies that used explicit and reproducible methods

Purpose: to deliver a meticulous summary of all the available primary research in response to a research question

Question 2

Identify the four steps involved in a systematic review

Answer 2

⇒ Systematic literature search

⇒ Selection of the materials

⇒ Appraisal

⇒ Synthesis

Question 3

What is a meta-analysis?

Answer 3

A meta-analysis is a quantitative synthesis of the results of two or more primary studies that addressed the same hypothesis in the same way

Question 4

Illustrate the relationship between a systematic review and a meta-analysis

Answer 4

A systematic review will not necessarily include a meta-analysis if, for example, clinical heterogeneity is too great

Question 5

State the four purposes of a meta-analysis

Answer 5

• To facilitate the synthesis of a large number of study results
• To systematically collate study results
• To reduce problems of interpretation due to variations in sampling
• To quantify effect sizes and their uncertainty as a pooled estimate

Question 6

To ensure quality criteria, a meta-analysis should have a formal protocol.

What should be specified?

Answer 6

• Compilation of complete set of studies
• Identification of common variable or category definition
• Standardised data extraction
• Analysis allowing for sources of variation

Question 7

How does one interpret a forest plot?

Answer 7

• Individual odds ratios (squares) with their 95% CI (lines) are displayed for each study
• Size of square is in proportion to the weight given to the study
• The (diamond) is the pooled estimate with the centre indicating the pooled odds ratio (dotted line) and the width representing the pooled 95% CI
• The (solid line) is the null hypothesis OR

Question 8

What are the three major problems with a meta-analysis?

Answer 8

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

Question 9

What is the reason for publication bias?

Answer 9

Studies with statistically significant / ‘favourable’ results are more likely to be published than those studies with non-statistically significant / ‘unfavourable’ results

Question 10

What are the consequences of publication bias?

Answer 10

• Any systematic review / meta-analysis can be flawed by such bias
• Publication bias leads to a biased selection of studies towards demonstration of effect

Question 11

Identify the three steps in the method of identification of publication bias in the selection of studies

Answer 11

⇒ Check meta-analysis protocol for method of identification of studies

⇒ Plot results of identified studies against a measure of their size i.e. a funnel plot

⇒ Use a statistical test for publication bias

Question 12

How might one interpret a funnel plot for publication bias?

Answer 12

• If no publication bias, then the plot will be a ‘balanced’/symmetrical funnel
• Smaller studies can be expected to vary further from the ‘central’ effect size
• Publication bias is likely to exist if there are few small studies with results indicating small or ‘negative’ measure of effect