Current Anaesthesia & Critical Care (2005) 16, 391–394 STATISTICS Systematic reviews & meta-analyses M.O. Columb à , A.-G. Lalkhen Acute Intensive Care Unit, South Manchester University Hospitals Trust, Wythenshawe, Manchester M23 9LT, UK KEYWORDS Systematic review; Meta-analysis; Evidence-based Summary Systematic reviews and meta-analyses are becoming more prevalent in the published literature and are routinely being used in the evidence-based approach to medicine. This article describes the process and methodology of conducting systematic reviews and meta-analyses and discusses the factors that affect the quality of the results and conclusions. & 2006 Elsevier Ltd. All rights reserved. Definitions Systematic review This is the formal process of identification, apprai- sal and evaluation of primary studies and other relevant research to draw conclusions about a specific issue. Meta-analysis This is the statistical discipline of assimilating data from similar smaller studies to measure an overall effect size with improved precision. Commonly it is invoked as part of a systematic review of the available literature. Rationale Modern medical practice demands the ‘conscien- tious, explicit and judicious use of current best evidence in making decisions about the care of individual patients’. 1 This ideal can easily be hampered in trying to keep pace with the expo- nential growth of research literature available. Traditionally the narrative review has been used as a means of providing a summary of available evidence to guide clinical decision-making. Narra- tive reviews however are subjective and therefore prone to bias and error. 2 The term meta-analysis was coined in 1976 by the psychologist, Gene Glass, to describe the statistical analysis of a large collection of results from individual studies. He described meta-analysis as the ‘analysis of ana- lyses. 3 The concept of combining studies to enable conclusions to be reached had been proposed as early as 1904 by Karl Pearson. 4 Meta-analysis has advantages over narrative re- views because it estimates the size of an effect, increases power and precision, and provides a rigorous framework for the appraisal of research. 5,6 The difference between a systematic review and a meta-analysis is that the latter represents a statistical integration of separate studies. 7 A systematic review is an overview of primary studies utilizing defined methods and criteria. 2,7 ARTICLE IN PRESS www.elsevier.com/locate/cacc 0953-7112/$ - see front matter & 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.cacc.2006.02.004 à Corresponding author. E-mail address: columbmo@msn.com (M.O. Columb).