METAANALYSIS - PRINCIPLES AND PROCEDURES

Meta-analysis should be as carefully planned as any other research pro ject, with a detailed written protocol being prepared in advance. The a priori definition of eligibility criteria for studies to be included and a comprehensive search for such studies are central to high quali ty meta-analysis. The graphical display of results from individual stu dies on a common scale is an important intermediate step, which allows a visual examination of the degree of heterogeneity between studies D ifferent statistical methods exist for combining the data, but there i s no single ''correct'' method. A thorough sensitivity analysis is ess ential to assess the robustness of combined estimates to different ass umptions and inclusion criteria.