25. Meta-analysis, systematic review
- These are the highest-quality studies
- No new data is collected; results from previous studies are combined
- Combining multiple studies reduces biases and improve statistical power
- Meta-analysis
- Data from multiple similar studies is processed with statistical methods
- Can be performed when there are multiple studies addressing the same question
- Answers questions like:
- What is the size of the effect?
- Is the effect consistent across studies?
- What is the strength of evidence for the effect?
- Steps
- Identify relevant studies and exclude poorly conducted studies
- Perform statistical analysis
- Which studies are included and which are excluded are very important for the validity of the results
- Systematic review
- Data from multiple similar studies is evaluated, but not necessarily processed with statistical methods
- Systematic review often include a meta-analysis
- Systematic review is needed because:
- There are way too many individual studies to keep in mind
- The sheer number of studies isn’t wanted; what is wanted is high-quality evidence
- Individual studies contain bias, which can be reduced by systematic review
- It produces a clear and consistent summary of the science on the question
- Often times different studies yield conflicting results, which a systematic review may yield information on
- May include unpublished data, to prevent publication bias
- Steps
- Defining an appropriate question
- Identify relevant studies and exclude poorly conducted studies
- Assess quality of each study or report
- Combine findings from the studies
- Interpret findings and present a balanced and impartial summary
- Data from multiple similar studies is evaluated, but not necessarily processed with statistical methods