Education and debate

Meta-analysis: Principles and procedures

^a Department of Social Medicine, University of Bristol, Bristol BS8 2PR, ^b Department of Primary Care and Population Sciences, Royal Free Hospital School of Medicine, London NW3 2PF

Correspondence to: Dr Eggerm egger@bristol.ac.uk

	Introduction

Meta-analysis is a statistical procedure that integrates the results of several independent studies considered to be "combinable."¹ Well conducted meta-analyses allow a more objective appraisal of the evidence than traditional narrative reviews, provide a more precise estimate of a treatment effect, and may explain heterogeneity between the results of individual studies.² Ill conducted meta-analyses, on the other hand, may be biased owing to exclusion of relevant studies or inclusion of inadequate studies.³ Misleading analyses can generally be avoided if a few basic principles are observed. In this article we discuss these principles, along with the practical steps in performing meta-analysis.

	Observational study of evidence

Meta-analysis should be viewed as an observational . . . [Full text of this article]

Summary points

	Standardised outcome measure

Odds ratio or relative risk?

	Statistical methods for calculating overall effect

	Bayesian meta-analysis

	Heterogeneity between study results

	Graphic display

	Relative and absolute measures of effect

	Sensitivity analysis

	Conclusions

	Acknowledgements

	Notes

	References

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