11 and 12 POP SCI- need to do Flashcards
What is a systematic review? What is the purpose of a systematic review?
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
Identify the four steps involved in a systematic review
⇒ Systematic literature search
⇒ Selection of the materials
⇒ Appraisal
⇒ Synthesis
What is a meta-analysis?
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
Illustrate the relationship between a systematic review and a meta-analysis
A systematic review will not necessarily include a meta-analysis if, for example, clinical heterogeneity is too great
State the four purposes of a meta-analysis
- 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
To ensure quality criteria, a meta-analysis should have a formal protocol.
What should be specified?
- Compilation of complete set of studies
- Identification of common variable or category definition
- Standardised data extraction
- Analysis allowing for sources of variation
How does one interpret a forest plot?
- 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
What are the three major problems with a meta-analysis?
- Heterogeneity between studies
- Variable quality of the studies
- Publication bias in selection of studie
What is the reason for publication bias?
Studies with statistically significant / ‘favourable’ results are more likely to be published than those studies with non-statistically significant / ‘unfavourable’ results
What are the consequences of publication bias?
- Any systematic review / meta-analysis can be flawed by such bias
- Publication bias leads to a biased selection of studies towards demonstration of effect
Identify the three steps in the method of identification of publication bias in the selection of studies
⇒ 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
How might one interpret a funnel plot for publication bias?
- 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