The investigators propose to develop and study partial effect-size indices for results of single and multilevel regression analyses and examine the suitability of the indices for use in meta-analysis. The investigators propose a program of work which combines mathematical statistics and simulation studies, illustrated with real educational examples. This work will provide guidelines that researchers can use in reporting results and effect sizes for complex primary-study analyses; facilitate meta-analyses of complex studies; and inform the conduct and reporting of primary studies in STEM research.