COLLABORATIVE RESEARCH: META-ANALYSIS: EVALUATION AND IMPROVEMENT OF AN IMPORTANT SYNTHETIC TOOL

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In environmental biology, different studies on the same topic can reach very different conclusions. Sometimes those disagreements are because of different methods or slightly different questions being answered, but other times they're due to true differences between years, places or species being studied. It is important that scientists be able to distinguish between these possibilities and confidently reach conclusions. For example, some studies suggest that growing different crops together results in higher overall yields for farmers, whereas other studies suggest that growing a single type of crop results in the highest yields. Do these conflicting results reflect some randomness in nature, different methods used by scientists in the two types of studies, or some other reason? A statistical approach called meta-analysis has been developed to solve this problem. Meta-analysis has helped many disciplines because it allows scientists to combine results from many studies, taking into account how they differ and providing insights that would otherwise remain hidden. This project will use advanced techniques to improve how meta-analyses are done. Researchers will focus on using the technique in the field of ecology. They will mentor students and a post-doctoral fellow in data collection and analysis. The results will be useful for improving the nation's ability to bring together and accurately interpret the complicated results of ecological studies. To improve the application of meta-analysis in ecology, this project will: 1) systematically review recent ecological meta-analyses to describe how they are typically performed (i.e., the statistical model and the way the size of an effect is calculated) and the characteristics of the dataset (e.g., the number of studies, the sample sizes of each study, and the magnitude of among-study and within-study variation); 2) use simulations to evaluate the performance of existing meta-analysis models and proposed alternatives (e.g., differing in weighting schemes, using Bayesian vs. frequentist approaches, or using different adjustments for non-independence), under a range of conditions likely to be encountered in ecological datasets (e.g., using sample sizes and the magnitudes of different sources of variation observed in ecology). Early career scientists engaged in this project will be trained in modern ecological methods, including meta-analysis. This project also will develop online materials that will be available publicly, thus helping educate ecologists across the nation in meta-analytic methods and improving the application of meta-analysis to ecological problems.