Meta analysis: An application on parallel controlled studies

In this first off all, concept of meta-analysis, its, historical development, aims, advantages and disadvantages, stages, the conception used in analysis, models and theatrical hypothesis information is given. Besides, meta-analysis is applied to the studies about the effect of probiotics to the weight of eggs in animal husbandry. In the research, the effect size calculation method is used by using the averages of continuous data for nine studies in the related literature and effect size about parallel - control model, publication bias, heterogeneity and general effect is calculated. As a result of the study, its determined that there is no publication bias and according to heterogeneity test all of the studies do not share one widespread impact (which shows heterogeneity). Also the result of general effect size showed that for the layer hens, probiotics has a significant effect on weight of the egg. Keywords: Meta analysis, Effect size, Fixed effect model, Random effect model.