Meta-analysis: A need for well-defined usage in ecology and conservation biology

Meta-analysis is a powerful research summarization technique. In the medical field, for example, meta-analysis is an indispensable tool as part of systematic reviews for healthcare decision making. The advantages of meta-analysis have also been recognized in the fields of ecology and conservation biology with the method becoming increasingly popular since the 1990s. ``Meta-analysis'', however, is not well-defined in these fields, but is regularly confused with other summary analysis techniques, such as multiple regression methods, vote-counting or other quantitative analyses. We argue that this vague and inconsistent utilization of the term is problematic, because a meta-analysis typically provides scientifically rigorous results. We therefore advocate a consistent and well-defined usage of the term in our disciplines, based on the standardized definition applied in the medical sciences. We searched the Web of Knowledge for meta-analyses in the subject area ``biodiversity conservation'' and evaluated the usage of the term ``meta-analysis''. Based on meta-analysis literature from the medical sciences, we determined steps that in our opinion are mandatory when performing meta-analysis and rated articles according to these steps. In the first round of rating, we assessed the usage of four `` technical'' steps that are normally applied in meta-analytical software. In the second round, we only evaluated the highly rated articles from the first round. We considered three steps regarding more qualitative aspects of interpretation and results presentation. Of the 133 evaluated articles in the first round, only 45% fulfilled all technical requirements for a meta-analysis, while 25% did not fulfill any of the requisite steps. In the second round, only one article of 83 fulfilled all requisite steps, while 22% did not fulfill any requirement. Our findings highlight the ambiguous and vague usage of the term ``meta-analysis'' in ecology and conservation biology and underline the importance of a consistent and clear definition. We conclude with recommendations on how the term should be applied in the future.