Meta-analysis in medicine: an introduction.

Meta-analysis, a complex statistical method which involves synthesis of data from relevant studies to devise an effect size or a conclusion, has increasingly been recognized and impacts on evidence-based medicine, especially in the field of health science. Thanks to the advent and unmet need of evidence-based medicine, since the first recordable publication of a meta-analysis in 1904 addressing the effectiveness of typhoid vaccine, both the number and quality of meta-analyses published relating to healthcare science have been on a steep rise. If properly conducted, based on answering relevant clinical questions, strict selection criteria of participating studies, appropriate analytical methods, and proper presentation of results, coupled with critical and faithful discussion on the strength and weakness of the analysis, meta-analysis will definitely be an invaluable tool for clinicians and researchers in understanding epidemiology, justifying and refining hypotheses of various diseases, for medical practitioners to implement sound management decisions based on evidence-based medicine, and ultimately, for policy-makers to formulate cost-efficient treatment strategies, guidelines and legislation. In this first paper of a mini-series, the current trend of meta-analysis publications in the medical literature, examples of important meta-analyses relevant to rheumatology and the pros and cons of meta-analysis, will be discussed. Important terminology related to meta-analysis, the systematic ways to critically appraise, and finally the preferred methodology of conducting meta-analysis will be covered in the subsequent three reviews of this mini-series.