Statistical issues in ecological meta-analyses

Meta-analysis is the use of statistical methods to summarize research findi ngs across studies. Special statistical methods are usually needed for meta -analysis, both because effect-size indexes are typically highly heterosced astic and because it is desirable to be able to distinguish between-study v ariance from within-study sampling-error variance. We outline a number of c onsiderations related to choosing methods for the meta-analysis of ecologic al data, including the choice of parametric vs. resampling methods, reasons for conducting weighted analyses where possible, and comparisons fixed vs. mixed models in categorical and regression-type analyses.