Meta-analysis in ecology

• Published in: Advances in Ecological Research Vol. 32; pp. 199 - 247
• Main Authors: Gurevitch, Jessica, Curtis, Peter S., Jones, Michael H.
• Format: Book Chapter Journal Article
• Language: English
• Published: London Elsevier Science & Technology 2001; San Diego, CA Academic Press
• Subjects: Animal, plant and microbial ecology; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; General aspects. Techniques; Generalities; Ecology; Statistical analysis; Review; Metaanalysis
• ISBN: 0120139324; 9780120139323
• ISSN: 0065-2504; 2163-582X
• DOI: 10.1016/S0065-2504(01)32013-5

Meta-analysis is the statistical synthesis of the results of separate studies. It was adapted from other disciplines for use in ecology and evolutionary biology beginning in the early 1990s, and, at the turn of the century, has begun to have a substantial impact on the way data are summarized in these fields. We identify 119 studies concerned with meta-analysis in ecology and evolution, the earliest published in 1991 and the most recent in 2000. We introduce the statistical methods used in modern meta-analysis with references to the well-developed literature in the field. These formal, statistically defensible methods have been established to determine average treatment effects across studies when a common research question is being investigated, to establish confidence limits around the average effect size, and to test for consistency or lack of agreement in effect size as well as explanations for differences in the magnitude of the effect among studies. Problems with popular but statistically flawed methods for the quantitative summary of research results have been pointed out, and their use is diminishing. We discuss a number of challenges and threats to the validity of meta-analysis in ecology and evolution. In particular, we examine how difficulties resulting from missing data, publication bias, data quality and data exclusion, non-independence among observations, and the combination of dissimilar data sets may affect the perceived utility of meta-analysis in these fields and the soundness of conclusions drawn from its application. We highlight particular applications of meta-analysis in ecology and evolution, discuss several controversies surrounding individual meta-analyses, and outline some of the practical issues involved in carrying out a meta-analysis. Finally, we suggest changes that would improve the quality of data synthesis in ecology and evolutionary biology, and predict future directions for this emerging enterprise.