JNEPHROL 2007; 20 (suppl 12): S1-S3 REVIEW S1 ABSTRACT Meta-analyses are frequently criticized because in most cases they are compiled from quite heterogeneous stud- ies. In spite of this limitation meta-analyses are increas- ingly published because in many areas of clinical re- search the results of individual studies are devoid of sta- tistical power and end up with conflicting results. Meta- analyses, if performed with a rigorous and exhaustive search of all accountable information on a specific topic, have the potential of overcoming the drawbacks of sin- gle studies and, in addition, of adjusting for publication bias and interstudy variability. These strengths of meta- analyses can be exploited to provide conclusive answers on diagnostic and therapeutic issues being debated, which in turn may help guide doctors toward more ratio- nal decisions. Key words: Benefits, Clinical trial, Hypertension, Meta- analysis INTRODUCTION In discussing the benefits of meta-analyses it is only fair to acknowledge in the first place that the scientific value of this method of a posteriori analysis is far from being unanimously recognized. Indeed meta-analyses are frequently blamed for “lumping together apples and oranges,” alluding to the het- erogeneity of the individual studies used for their compilation, while their authors are sometimes accused of exploiting the work of other, more creative investigators. Yet, despite these harsh criticisms, meta-analyses are increasingly appreciated by readers of scientific journals, as can be seen from the fact that, according to a Medline search, the number of those published rose steadily during the years 2000 to 2005. The most likely reason for the increasing success of meta-analy- ses is that in some specific areas the results of single trials may not provide sufficient evidence, or their results are even conflicting. Thus meta-analyses are often performed to over- come the limits of individual trials and to generate a consen- sus on issues under debate. Therefore, in this view, they may indeed represent a useful support to clinical research. Herein, I will briefly summarize the strengths of meta-analyses and present a few examples of some recent ones which, in my opinion, have contributed to solve some unsettled questions in the diagnosis and treatment of hypertensive patients. DEFINITION AND POTENTIALITIES OF META-ANALYSES Most pitfalls of meta-analyses derive from the inaccuracy and incompleteness of data collection; these limitations could be overcome if meta-analyses were carried out according to the precise and comprehensive definition recently proposed by Schork (1): “A meta-analysis is a review of all the literature on a specific topic which includes statistical accountability of interstudy variability; a quantita- tive rigorous investigation of published summary information from an exhaustive list of studies relevant to a medical issue.” When the requirements outlined in this definition are satisfied, the meta-analysis may indeed become a powerful tool because the combination of numerous studies enhances their statistical power; in addition, meta-analyses can adjust for publication bias and for the characteristics of various studies and provide a complete and easy instrument for review and comparison. A list of the topics for which the meta-analytic approach may be particularly useful is shown in Table I. Alberto Morganti Chair of Internal Medicine and Hypertension Center, Ospedale San Giuseppe Fatebenefratelli - Milano Cuore; Center of Clinical Physiology and Hypertension, IRCCS Ospedale Maggiore, University of Milan, Milan - Italy The impact of meta-analyses on clinical practice: the benefits www.sin-italy.org/jnonline – www.jnephrol.com