1 Place of Meta - analysis among other Methods of research synthesis

in the moSt general terms, meta-analysis is one method of research synthesis. Research synthesis may be defined as a review of primary research on a given topic with the purpose of integrating the findings (e.g., for creating generalizations or resolving conflicts). Research synthesis is central to the scientific enterprise. Without it, the evidence for various alternative hypotheses cannot be properly evaluated and generalizations cannot be reached, thus the advance of the scientific field as well as any potential practical applications are inhibited. Research synthesis can be performed either qualitatively, in the form of a narrative review, or quantitatively, by employing various statistical methods for the integration of results from individual studies. Research reviews in ecology and evolutionary biology have traditionally been carried out either in the form of narrative reviews, or by " vote counting, " where the number of statistically significant results for and against a hypothesis are counted and weighed against each other (see below). In other fields, it has been widely recognized that neither of the above methods is adequate to address current needs for quantitative research synthesis, and we believe that this is also true in ecology, evolution, and conservation biology. Narrative reviewing offers expert interpretation and perspective, but it is inherently subjective and nonquantitative. Vote counting has very poor properties as a statistical procedure, as discussed below. Neither procedure is able to provide critically important information on the magnitude of the effects or the sources of variation in outcomes among studies. The lack of training in formal, rigorous protocols for research synthesis in ecology and evolutionary biology contrasts markedly with the standard quantitative training that scientists in these fields receive for primary research, including training in experimental design and analysis. Fortunately, this asymmetry in the tools employed for primary versus synthetic investigations began to change dramatically in the past two decades as meta-analytic methods have started to be introduced and incorporated into standard practice. The summarization and integration of research results across studies is increasingly viewed as a scientific research process in its own right in ecology and evolutionary biology, as it has come to be recognized in other disciplines. Like primary research, research synthesis follows the scientific method and is held to scientific standards. Meta-analysis employs specialized techniques for data gathering and analysis developed specifically for the purposes of research synthesis. Below, we briefly review the variety of approaches to research synthesis and discuss …