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What is meta-analysis?
  1. Allison Shorten1,
  2. Brett Shorten2
  1. 1School of Nursing, Yale University, New Haven, Connecticut, USA
  2. 2Informed Health Choices Trust, Wollongong, New South Wales, Australia
  1. Correspondence to : Dr Allison Shorten
    Yale University School of Nursing, 100 Church Street South, PO Box 9740, New Haven, CT 06536, USA; allison.shorten{at}

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When clinicians begin their search for the best available evidence to inform decision-making, they are usually directed to the top of the ‘evidence pyramid’ to find out whether a systematic review and meta-analysis have been conducted. The Cochrane Library1 is fast filling with systematic reviews and meta-analyses that aim to answer important clinical questions and provide the most reliable evidence to inform practice and research. So what is meta-analysis and how can it contribute to practice?

What is meta-analysis?

Meta-analysis is a research process used to systematically synthesise or merge the findings of single, independent studies, using statistical methods to calculate an overall or ‘absolute’ effect.2 Meta-analysis does not simply pool data from smaller studies to achieve a larger sample size. Analysts use well recognised, systematic methods to account for differences in sample size, variability (heterogeneity) in study approach and findings (treatment effects) and test how sensitive their results are to their own systematic review protocol (study selection and statistical analysis).2 ,3

The Five-step process

There is debate about the best practice for meta-analysis, however there are five common steps.

Step 1: the research question

A clinical research question is identified and a hypothesis proposed. The likely clinical significance is explained and the study design and analytical plan are justified.

Step 2: systematic review

A systematic review (SR) is specifically designed to address the research question and conducted …

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