Post 7: Systematic Reviews & Meta-Analyses

Both systematic reviews and meta-analyses are key elements of evidence-based healthcare.  A systematic review answers a defined research question by collecting and summarising all empirical evidence that fits the criteria¹ and a meta-analysis is the use of statistical methods to aggregate data and summarise results from these studies².   

A systematic review is determined in five steps:

1.     Determine the question to be answered

The question needs to be easy to follow and once set, then modifications can be made to the protocol, but only if changes in populations, outcomes or study designs is necessary³.

2.     Identify relevant studies

Extensive research needs to be done for studies, reasons for and against studies needs to be recorded⁴.

3.     Assess the quality of the studies

Selected studies need to be compared to a specific checklist of assessments to allow informed decisions and to assess the strength of any negative implications and/or recommendations for future work.

4.     Summarise the evidence

Data from the studies need to be analysed; this will include study characteristics, the quality of each individual studies, effects found in the studies, and the use of statistical methods to explore differences between studies and then the combination of the effects (meta-analysis).

5.     Understanding the findings

Biased nature will need to be determined, any effects observed in the studies can be used to create conclusions, and recommendations will be determined in reference to the strengths and weaknesses found in the evidence.

 Explore the above YouTube videos on how to critically appraise a Systematic Review: Parts 1 & 2

Unlike meta-analysis, systematic reviews don’t employ quantitative methods to summarise results⁵. The exhaustive and powerful review process, while less costly and less time consuming than creating a new study, is subject to possible bias that lies in identifying relevant studies and choosing the studies to be included⁴ thereby enhancing the validity of the results and provides a summary of the findings.    A meta-analysis combines pertinent data from several studies to develop a single conclusion that has greater statistical power offered from the best available syntheses of evidence. 

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1  Centre for Cognitice Ageing and Cognitive Epiemiology.  Systematic reviews and meta-analyses: a step-by-step guide. [internet] University of Edinburgh. 2013; [cited May 8 2015]. Available from http://www.ccace.ed.ac.uk/research/software-resources/systematic-reviews-and-meta-analyses

2  Egger M. Meta-analysis: Principles and procedures. BMJ 1997; 315(1533) [cited May 8 2015]. Available from http://www.bmj.com/content/315/7121/1533

3  Kahn K Kunz R Kleijnen J Andes G. Five steps to conducting a systematic review. J Roy Soc Med; 96:118-121

4  Walker E Hernandez AV Kattan MW. Meta-analysis: It’s strengths and limitations. Clev Clin J Med; 2008; 75(6):431-439

5   Gerstman B.  Epidemiology kept simple: An Introduction to traditional and modern epidemiology, 3rd ed; Hoboken, USA; Wiley; 2013